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, the pressure to make immediate decisions often drives us to accept the first recognizable image that appears on the screen. When managing undifferentiated shock, a rushed, oblique view can easily mimic hypovolemia, tempting you to rapidly push fluids into a patient who might actually be in cardiogenic failure. The goal of focused cardiac ultrasound is not to delay care in pursuit of a pristine, formal echocardiogram, but to ensure the image is anatomically honest. Taking three extra seconds to make a millimeter adjustment doesn’t delay resuscitation; it prevents a potentially catastrophic intervention based on an ultrasound artifact.
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.
The usual basic windows are:
Subcostal → PLAX → PSAX → A4C → IVC
ACEP’s focused cardiac reporting framework also recognizes these standard views.
But obtaining “something that looks like the heart” is not enough.
The real skill is knowing whether the plane is trustworthy.
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.”
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 sequential anatomy:
RV near field → interventricular septum → LV → mitral valve → LVOT/aortic valve → 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.
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.
3. PSAX: make the LV round before interpreting it
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.
For rapid assessment of global LV systolic function, the midventricular papillary-muscle level is particularly useful. ACEP’s Sonoguide similarly identifies this as the commonly used short-axis level in acute-care POCUS.
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
A proper midventricular short-axis LV should look approximately circular.
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:
Make it round before you interpret it.
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.
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
That is a foreshortened LV.
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.
But no single feature should substitute for understanding the anatomy.
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 cutting a cylindrical tube diagonally rather than through its central axis.
The apparent diameter changes.
The same thing happens when the ultrasound beam is off-axis.
You may measure a portion of the IVC that is not its true maximal diameter and conclude that the vessel is smaller than it actually is.
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.
The exact convention matters less than being consistent and understanding what you are measuring.
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.
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?
“Make it round before interpreting it.”
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.
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?
Only after those three questions should the image begin changing management.
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.
Video demonstrations
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.
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.
For PLAX, this recent bedside-oriented tutorial specifically covers probe positioning, opening/elongating the LV and correcting poor images.
For PSAX, the MedStar Georgetown tutorial is particularly suitable for your teaching objective because it demonstrates movement through the aortic, mitral and papillary-muscle levels rather than presenting PSAX as a single static image.
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.
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.
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.
