The Quick and Dirty Guide to Heart Tones

What are they, Where are they, and What are they for?

Where to Listen

The location for auscultation of each heart sound is in the diagram above.
(M) Mitral (T) Tricuspid (A) Aortic (P) Pulmonic. The blue area is the pleura, pink is lung, red outline is heart.

Why should I care about heart sounds?

You can use heart tones in combination with other clinical findings to create a differential diagnosis and begin to treat heart failure and other cardiac pathologies en route. You can also provide a better picture to the ED, so they can treat your patient faster and more accurately. Paramedics and EMTs who know and listen to heart tones are the CSI team of cardiac EMS! By knowing what's going on (or not going on) when you hear these sounds, it will make you a better medic. Its not hard, and you want to be a rock star, so learn them and practice them all the time. You're not going to be able to pick out bad heart tones until you've listened to normal heart tones hundreds of times. As with everything clinical, practice practice, practice!


The two beats you should hear on a "normal" patient are called "Sound 1" and "Sound 2." We shorten this to S1 and S2. They are the two "Lub dub" beats you hear in a normal heartbeat.


The First Heart sound  (S1) "Lub"  is caused by the closing of the Mitral (Bicuspid) and Tricuspid atrioventricular valves.  If you want to review, we talked more about valves in our Quick and Dirty Guide to Cardiology I.  The first sound (S1, Lub) is caused by blood slamming shut these valves. They generally shut at the same time in healthy patients so you only hear one nice distinct "Lub" The mitral side is operating at a much higher pressure, so the sound will mostly be coming from it. Sometimes, when the two atrioventricular valves aren't shutting at the same time, you can hear them both, with the tricuspid sound much quieter. When this happens, its called a Split S1, and it is normal for about 40% of patients. Split S1 is also common in RBBB because of conduction delays. The time that you hear the S1 represents the beginning of systole (when the heart flexes ventricular muscle and SQUEEZES the blood out of it. [Systole = Squeeze].

The Second Heart sound (S2) "Dub" is caused by blood slamming shut of the semilunar valves (Aortic and Pulmonic). They generally shut at the same time in healthy patients so you only hear one nice distinct "Dub."  The left side (Aortic valve) is the loud one here because the left side of the heart is the high pressure side. Just like S1, these sounds can be split. The S2 sound means blood has left the ventricle and is no longer being allowed back in, so it represents the end of ventricular systole [systole =squeeze.]

Pro Tip: In Tachycardic (fast heart rate) patients, the two sounds "LUB DUB" sound the same sometimes and its hard to distinguish them. When you can't tell which is which, feel a pulse while you're listening. The Pulse is felt on every S1.

1.5 minute short video summarizing 1-2 again, so you can hear it and see it.


The Third Heart Sound (S3) "Ta"  is short and called "ta." Its known as a ventricular gallop because it makes the heart tones sound like a horse galloping.  S3 is the sound of blood sloshing around in a compliant left ventricle. It occurs directly after "Dub" and is a lower pitch than "Dub." It can be an important sign of heart failure. The best place to listen for an S3 is at the cardiac apex. (M in diagram)

Take 55 seconds and listen/watch S3 in action


The Fourth Heart Sound (S4) is rare. The best way to remember it is that it sounds like a gallop where the loudest sound (s1) comes in the middle. So, it sounds like Ta-LUB-dub, ta-LUB-dub. The S4 sound is usually caused by a failing left ventricle and is best heard at the cardiac apex.

Take 55 seconds and listen/watch S4 in action

 Murmurs and Rubs


A murmur is simply the sound of turbulent blood flowing through an incompetent valve. Sometimes hardening of the valve (stenosis) causes it to be unable to fully open or close, so blood is able to backflow against it. This is called regurgitation. It sounds like a miniature version of putting your thumb over the water hose.  Here is a chart to where and when you will hear the murmur and to the condition with which it is associated. For the most part, just remember that a murmur is turbulent blood flow through a failing valve. Depending on where its heard and at what stage of lub-dub, you can predict which valve it is!

Quick Reference

As an example, here is the sound of a mitral valve regurge with a picture so you can see and hear that the blood is leaking back into the left atrium!

Pericardial Friction Rub

Pericardial friction rubs are the sounds of two layers of the pericardium rubbing together. It sounds awful and is loudest during systole (between the lub and dub) It is indicative of pericarditis (inflammation of the pericardium) and your patient is usually a chest pain CC. You can also see signs of pericarditis on a 12 lead (more about that in ECG lessons.) Pericarditis is also a significant STEMI imposter, so listening for a friction rub can be an important part of your differential diagnosis!


Take 55 Seconds and listen to a Pericardial Friction Rub

Test Yourself 

Practice checking for s1, s2, splits, extra sounds and murmurs with this interactive online game. Very Helpful! 

Want more?? Heart Tones tutorial (Amazing!) 

Wikipedia Page on Heart Sounds

Advanced Murmur Videos explaining a TON of information about murmurs and their diagnostic capability
Part 2: Murmur Pitch
Part 3: Putting it all together's Quick and Dirty Guide to Heart Failure