How to interpret a PCG and spot a murmur

The Eko App allows you to visualize normal and abnormal heart sounds taken with an Eko device. Here you’ll learn the basics about interpreting a PCG and spotting a murmur.

About PCG

A phonocardiogram (PCG) is a waveform of heart sounds. It’s a two-dimensional plot of sound intensity (loudness) versus time. Sound intensity is shown on the Y-axis, and time is shown on the X-axis. PCGs allow you to visually group sounds with more ease than when using your ear alone.

The two fundamental heart sounds, S1 and S2, are shown on a PCG as large magnitude deflections occurring one after the other. S1 marks the beginning of systole; S2 marks the beginning of diastole. Depending upon where on the body the sounds were captured, the S1 deflection may be larger, S2 may be larger, or the sounds may be the same size (loudness). At other times the heart is silent, so the PCG will be flat.


Here’s a PCG showing the intensity of sound on the Y-axis and time on the X-axis. S1 is the first heart sound and S2 is the second heart sound.


PCGs in the Eko App

When the Eko CORE is connected to the Eko App, you can perform an exam and view the PCG. A PCG recording in the Eko App can be played back, saved, and shared.


Abnormal heart sounds

Certain heart conditions are associated with additional, abnormal heart sounds. Murmurs are the most common abnormal heart sounds, such as aortic stenosis, mitral regurgitation, aortic regurgitation, and mitral stenosis. Less commonly, a third heart sound (S3) and/or a fourth heart sound (S4) may be present. S3 and S4 are associated with acute, decompensated heart failure. Other abnormal sounds include clicks and rubs.

Once S1 and S2 are identified, abnormal sounds can be put into their correct positions in the cardiac cycle.


Here are PCG examples of each of these murmurs, as well as a normal heart sound.

Normal heart sound


Aortic stenosis (AS)

AS causes a crescendo-decrescendo, systolic ejection murmur that is best heard at the upper right sternal border.


Aortic regurgitation (AR)

AR causes a high-pitched, decrescendo diastolic murmur best heard in the second intercostal space at the left sternal border.


Mitral regurgitation (MR)

MR causes a high-pitched, holosystolic murmur best heard at the apex.


Mitral stenosis (MS)

MS causes a low-pitched diastolic murmur best heard at the cardiac apex. The murmur is preceded by a unique “opening snap.”


Learn more

To learn more in-depth about PCGs, see Phonocardiograms (PCG) in Eko Academy.


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Date of Issue:

November 30, 2022

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