During cardiac POCUS, the image shows a very small LV. Vigorous contraction. Almost complete cavity obliteration.
The learner looks at the PLAX and says:
“This patient is profoundly hypovolemic.”
Maybe.
But before accepting the physiology, I want to ask a more basic question:
Is this actually a valid PLAX?
Because if the imaging plane is oblique, the LV can look artificially narrow, small, and impressively contractile.
This is one of the most important lessons when teaching focused cardiac ultrasound:
Do not interpret pathology until you trust the imaging plane.
The purpose of basic cardiac POCUS is not to turn emergency physicians into comprehensive echocardiographers. It is to obtain technically valid views, recognize major physiological patterns, and understand when the image is not reliable enough to support the conclusion.
That distinction matters.
In the resuscitation bay, an oblique view can lead to an incorrect physiological conclusion. Make brief image adjustments when they are safe, while ongoing treatment continues. During cardiac arrest, a skilled operator must not add or prolong interruptions in chest compressions to obtain or optimize a view; record a brief clip within the planned check and interpret it after compressions resume. Image quality matters, but it must not delay a time-critical intervention. See AHA 2025 ALS guidance.
Cardiac POCUS fundamentals
What are we actually trying to do with focused cardiac ultrasound?
Focused cardiac ultrasound answers specific bedside questions.
Depending on the patient, we may be asking:
- Is there significant pericardial fluid?
- Is LV systolic function grossly reduced or preserved?
- Is the RV obviously enlarged or dysfunctional?
- Are the ventricles severely underfilled?
- Is there cardiac activity during arrest?
- Is there a pattern suggesting obstructive, cardiogenic, distributive, or hypovolemic physiology?
Focused cardiac ultrasound should therefore be treated as an extension of the clinical examination, not as an isolated image interpreted outside the patient’s physiology. ACEP similarly describes emergency cardiac ultrasound as a focused examination used with the history, examination, laboratory data, and resuscitation context.
Use broad visual categories for LV systolic function; do not assign a precise EF from an unmeasured clip. A technically limited scan is inconclusive. Persistent symptoms, uncertain findings or a mismatch with the clinical picture require further assessment, often comprehensive echocardiography. A preserved-looking LV does not exclude heart failure. See the ASE focused cardiac ultrasound recommendations.
The usual basic windows are:
Subcostal → PLAX → PSAX → A4C → IVC
These are standard windows, not a compulsory scanning order. Confirm the probe marker and screen orientation for the selected preset before applying a tutorial’s directions.
But obtaining “something that looks like the heart” is not enough.
The real skill is knowing whether the plane is trustworthy.
For the basic orientation before the station, this Stanford Medicine 25 video is particularly useful because probe position and the ultrasound image are demonstrated simultaneously, and it covers PLAX/PSAX, A4C and subcostal acquisition in one sequence.
Watch Cardiac POCUS overview directly on YouTube.
A quick language for probe movement
Before discussing the views, learners need a shared vocabulary.
Slide: Move the entire probe across the skin.
Rotate: Turn the probe around its central axis.
Tilt / fan: Keep the footprint approximately in place and change the direction of the ultrasound beam.
Rock: Angulate the probe along its long dimension.
And perhaps the most useful instruction for beginners:
Once you have found the heart: millimetres, not centimetres.
Large movements repeatedly destroy good windows.
Most optimization happens with surprisingly small adjustments.
1. Subcostal four-chamber: use the liver, then aim toward the chest
The beginner places the probe just below the xiphoid.
The screen shows liver.
They slide.
Still liver.
They slide again.
Still liver.
The problem may not be the position.
It may be the angle.
The transducer face is often too vertical, so the beam is travelling posteriorly into the abdomen rather than superiorly beneath the sternum toward the heart.
My correction is:
“Keep your hand there. Flatten the probe and aim under the sternum toward the heart.”
The liver is useful. It is the acoustic window.
But we need to look through it toward the thorax, not deeper into the abdomen. The standard subxiphoid technique similarly uses the liver as the acoustic window while angling toward the heart.
Once a portion of the heart appears, stop making dramatic movements.
“You have the heart. Now millimetres, not centimetres.”
Then gently fan through the chambers.
The subtle trap
Seeing all four chambers does not automatically mean that the plane is correct.
A foreshortened or oblique subcostal cut can alter LV geometry and make contraction look more impressive.
So before saying:
“Good LV.”
Ask:
“Is this a reasonably long LV in a believable four-chamber geometry?”
That small pause prevents a surprising amount of overinterpretation.
Bedside rescue
When hyperinflated lungs make parasternal imaging frustrating, particularly in patients with COPD, the subcostal window may still be excellent.
A poor parasternal window therefore does not mean:
“This patient has poor echo windows.”
It means:
“Try another window.”
For subcostal troubleshooting, I would use the short Stanford “common mistakes” video. The subcostal section starts at about 4:24, and the same video is valuable for demonstrating why small acquisition errors matter across the other windows as well.
Watch Common acquisition mistakes directly on YouTube.
2. PLAX: a narrow LV may be your imaging plane
For beginners, PLAX is one of the most useful windows for judging gross LV function.
But it also contains an important trap.
You can create an image that resembles PLAX while cutting obliquely through the ventricle.
The result may be:
short LV → narrow cavity → apparently vigorous contraction
The learner sees this and thinks:
Hyperdynamic.
Then:
Hypovolemic.
But the first diagnosis may actually be:
off-axis PLAX.
What am I looking for?
I want a long LV cavity with recognizable landmarks:
Near-field RV, interventricular septum, LV cavity and posterior wall, mitral valve, LVOT/aortic valve, and left atrium.
The simplest teaching instruction is:
“Open the LV. Give me its longest axis.”
If the LV looks narrow, do not immediately abandon the window.
Start with:
small rotation + small tilt
and watch whether the LV cavity lengthens.
Only after that should you consider moving to another intercostal space or changing patient position.
Left lateral positioning and respiratory adjustment can also improve parasternal imaging when lung interferes with the acoustic window.
The wrong view can still be a good image
Sometimes the learner fans away from standard PLAX and suddenly shows the right atrium and tricuspid valve beautifully.
Rather than saying:
“That’s a bad image.”
I prefer:
“That’s actually an RV inflow view. You acquired another view correctly. Now fan back until PLAX returns.”
That teaches spatial anatomy instead of simply labelling the attempt a failure.
One more caution
PLAX does not display the entire LV. The true apex is usually outside this plane; lengthen the cavity without trying to manufacture an apex. See the ASE acquisition guidance.
Regional dysfunction may therefore distort your impression of global function.
This is why cardiac POCUS should be corroborated in more than one window whenever possible. ACEP similarly recommends attempting all focused cardiac views rather than relying on a single image.
Never fall in love with one view.
For PLAX, the POCUS Pearls tutorial covers probe positioning, lengthening the LV and correcting common acquisition errors.
Watch Parasternal long-axis tutorial directly on YouTube.
3. PSAX: verify the plane before interpreting LV shape
From a good PLAX, rotate approximately 90 degrees and you enter the short-axis family of views.
And that distinction matters:
There is not one PSAX.
As you fan from base toward apex, you may encounter:
aortic valve → mitral valve → papillary muscles → apex.
The papillary-muscle level is a useful starting point for visual LV assessment. Sweep through the base, midventricle and apex, then compare with long-axis views. One short-axis slice cannot establish global function or exclude regional dysfunction.
The beginner trap: wrong level
The learner produces a beautiful circular LV.
But the mitral leaflets are visible.
That is not the same physiological slice as the papillary-muscle level.
Or they move too far toward the apex.
The apparent degree of contraction changes as the imaging level changes.
So for visual LV assessment:
Find the papillary muscles first.
Only then interpret contraction.
The second trap: an oval LV
In a normal heart, a true midventricular short-axis LV is approximately circular. An elliptical image should prompt a check for an oblique plane, but genuine septal flattening can persist in a correctly acquired view. Assess the timing of flattening and the accompanying RV findings rather than trying to force the LV to look round.
If it is strongly elliptical, first ask whether the plane is oblique.
This matters because an oblique PSAX can potentially create the impression of abnormal septal shape.
And now the clinician may say:
“D-sign. RV pressure overload.”
Maybe.
But before diagnosing RV pressure overload:
Confirm a perpendicular short-axis plane before interpreting shape; do not optimize away genuine septal flattening.
This is particularly important because septal geometry carries major clinical implications in patients with shock, dyspnea, and suspected pulmonary embolism.
How to navigate PSAX
Remember:
Rotate to enter PSAX.
Then:
Tilt/fan to choose the level.
Do not start randomly sliding across the chest every time the papillary muscles disappear.
For PSAX, the MedStar Georgetown tutorial covers orientation and movement through the aortic, mitral and papillary-muscle levels.
Watch Parasternal short-axis tutorial directly on YouTube.
4. A4C: find the true apex before comparing chambers
The apical four-chamber view is extremely useful.
It is also unforgiving.
The major enemy is foreshortening.
A true apical view begins from the actual apex of the LV.
The normal LV should look long and tapered.
When the probe is too medial or too cephalad, the true apex is missed.
The LV then looks:
short + round + spherical
Check for foreshortening. A rounded LV can also reflect genuine remodeling; shape alone does not establish an acquisition error.
And this is not merely an aesthetic problem.
It can change your interpretation of ventricular size and systolic function.
The practical correction
If the LV looks short:
move more inferiorly and laterally toward the true PMI/apex.
Then flatten and fan until you obtain the maximal LV length.
My teaching phrase is:
“Find the apex first. Then build the four-chamber view around it.”
Left lateral positioning frequently helps because it brings the heart closer to the chest wall. Apical acquisition guidance similarly emphasizes locating the PMI/apex and minimizing foreshortening.
Why this matters particularly for the RV
A4C is commonly used to compare RV and LV size.
That makes poor acquisition dangerous.
If the LV is foreshortened, the chamber comparison is no longer trustworthy.
So before saying:
“The RV is dilated.”
Ask:
“Do I actually have a valid apical plane?”
And remember that the standard A4C is not identical to an intentionally acquired RV-focused A4C.
Identifying the RV
Useful clues include:
- thinner wall,
- more trabeculation,
- moderator band,
- and slightly more apical insertion of the tricuspid valve compared with the mitral valve.
These are typical features; disease can alter wall thickness. No single feature should substitute for understanding the anatomy.
For A4C, the Sonosite 3D animation is useful because learners can visualize the relationship between probe position, imaging plane and the resulting four-chamber slice—exactly what they need to understand foreshortening.
Watch Apical four-chamber demonstration directly on YouTube.
5. The IVC: technically easy to find, physiologically easy to misuse
The IVC deserves special attention because acquisition errors and interpretation errors frequently occur together.
First question: is that actually the IVC?
Do not identify a vessel simply because it is black and tubular.
Prove it anatomically.
Follow it through the liver toward its entry into the right atrium.
A hepatic vein joining the vessel provides another useful landmark.
The aorta behaves differently: it has a thicker wall, is more pulsatile, and does not enter the right atrium.
My instruction is:
“Don’t tell me it’s the IVC. Show me where it goes.”
The cylinder effect
Imagine viewing the edge of a tube rather than its center.
A tangential long-axis cut can make the lumen look smaller. Other oblique cuts distort geometry differently, so an off-axis view does not always underestimate diameter.
Confirm the central long axis and measure across the vessel, perpendicular to its walls.
So:
“Center the vessel before you measure the vessel.”
Use small rotations and tilts until the lumen is convincingly centered.
Standardize where you measure
If you are using diameter or respiratory variation, use a reproducible region near the cavoatrial junction rather than choosing an arbitrary abdominal segment.
ACEP describes measurements roughly 2–3 cm from the right atrium or just distal to hepatic-vein insertion.
Use the same validated measurement convention when applying a cutoff or following a trend. The 2025 ASE right-heart guidance measures IVC diameter at end-expiration in a standardized subcostal plane, approximately 0.5–3.0 cm from the RA ostium and distal to the hepatic vein. Confirm that apparent respiratory variation is not simply vessel translation out of the imaging plane. Do not interchange measurement sites or breathing maneuvers without considering their effect.
The dangerous statement: “collapsible IVC means fluids”
This is where physiology becomes essential.
In spontaneous inspiration, negative intrathoracic pressure increases venous return and can decrease IVC diameter.
But the magnitude of that change depends on more than circulating volume.
A patient taking forceful inspiratory breaths may generate substantial IVC collapse simply because respiratory effort is high.
Mechanical ventilation changes the physiology again because positive intrathoracic pressure changes venous return and IVC behaviour.
Therefore, before interpreting the IVC:
Look at the patient breathing.
Not just the ultrasound screen.
And do not use the IVC alone to prescribe fluid
A small collapsible IVC is not synonymous with “give one litre.”
A plethoric IVC is not synonymous with “never give fluid.”
Right-sided filling pressure, respiratory mechanics, RV failure, tamponade physiology, positive-pressure ventilation, intra-abdominal pressure, and other factors may all influence its appearance.
ACEP’s shock guidance similarly cautions that multiple variables affect IVC size and collapsibility and may produce misleading conclusions when the finding is used in isolation.
A safer statement is:
“The IVC gives me information about right-sided filling conditions and cardiopulmonary interaction. I will integrate it with the heart, lungs, perfusion and the clinical response.”
That is much closer to the way we should actually use POCUS during resuscitation.
For the IVC, Stanford’s dedicated video is considerably more detailed than most quick tutorials. It covers positioning, acquisition, troubleshooting and an alternative transhepatic approach.
Watch Inferior vena cava demonstration directly on YouTube.
The five corrections I want faculty to remember
When supervising a hands-on station, you do not need a long lecture while the learner is scanning.
You need one useful correction.
Subcostal:
Only liver or partial heart?
“Flatten and aim toward the chest.”
PLAX:
LV looks short or narrow?
“Open the LV. Find its longest axis.”
PSAX:
LV looks oval?
“Confirm the short-axis plane, then interpret the shape.”
A4C:
LV looks short and spherical?
“Find the true apex first.”
IVC:
Not sure about the vessel or plane?
“Follow it into the RA and center the vessel.”
These short instructions work because each one corrects the geometry before asking the learner to interpret physiology.
Back to our patient
The learner shows a tiny, vigorously contracting LV on PLAX and says:
“This patient is profoundly hypovolemic.”
I would challenge two things immediately.
1. Is the PLAX actually on-axis?
A narrow oblique cut can create an artificially small LV and exaggerate the apparent contraction.
Before diagnosing physiology:
open the LV and obtain its true long axis.
2. Even if the LV truly is small and hyperdynamic, does that prove hypovolemia?
No.
A hyperdynamic LV tells us something about the current relationship between chamber loading, contractility, and afterload.
That pattern may occur with low preload, but it can also be seen in vasodilatory/distributive physiology and other high-catecholamine states.
EF describes the fraction of end-diastolic volume ejected. A small LV may eject a large fraction yet deliver a small stroke volume. Brisk cavity emptying therefore does not establish adequate forward flow or fluid responsiveness. Quantitative EF needs appropriate images and measurements. See the ASE/EACVI chamber-quantification guidance.
So now I want more information:
What does the RV look like?
What do the lungs show?
What is the IVC doing, and how is the patient breathing?
What is the blood pressure pattern?
What does peripheral perfusion look like?
What happened after the last intervention?
POCUS becomes useful when it modifies physiological probability.
It becomes dangerous when one attractive image becomes the diagnosis.
The practical cardiac POCUS rule
Whenever an ultrasound finding seems dramatic, resist the temptation to interpret it immediately.
First ask:
Is the view technically valid?
Then:
Does the finding persist in another view?
Then:
Does it make physiological sense in this patient?
Use these questions to calibrate confidence while treatment continues. Do not delay a time-critical intervention to complete every view. If the scan remains limited, document the uncertainty and seek the imaging or expertise needed to answer the clinical question.
That is the real skill we are trying to teach.
Image quality comes before interpretation.
Continue learning: Apply these acquisition principles during shock assessment in Understanding RUSH 2.0 and From Scan to Action.
References
- Prats MI, Bahner DP. Cardiac. ACEP Sonoguide. Updated August 18, 2020.
- Spencer KT, et al. Focused Cardiac Ultrasound: Recommendations from the American Society of Echocardiography. J Am Soc Echocardiogr. 2013;26:567–581.
- Mukherjee M, et al. Guidelines for the Echocardiographic Assessment of the Right Heart in Adults. J Am Soc Echocardiogr. 2025.
- Mitchell C, et al. Guidelines for Performing a Comprehensive Transthoracic Echocardiographic Examination in Adults. J Am Soc Echocardiogr. 2019;32:1–64. doi:10.1016/j.echo.2018.06.004.
- Lang RM, et al. Recommendations for Cardiac Chamber Quantification by Echocardiography in Adults. J Am Soc Echocardiogr. 2015;28:1–39.e14. doi:10.1016/j.echo.2014.10.003.
- ACEP Sonoguide. Rapid Ultrasound for Shock and Hypotension (RUSH).
