Abnormal heart sounds

If you put a stethoscope over the chest, you’ll usually hear something that sounds like lub dub, lub dub, lub dub, which repeats over and over again, with each cardiac cycle, or heartbeat.

In total, our heart has four valves- two atrioventricular valves, between the atria and the ventricles, which are the tricuspid valve, on the Left side, and the mitral valve, on the left side, and two semilunar valves, between the ventricles and the large arteries coming off of them, which are the pulmonary valve, on the right side, and the aortic valve, on the left side. Normally, in every heartbeat, some valves open, allowing blood to pass through and others close to hold blood within a chamber. The sound of the closing of each of these valves is projected onto the chest wall. The two normal heart sounds are S1, which is basically the tricuspid and mitral valve closing, and S2 which is the aortic and pulmonic valve closing. Between S1 and S2, we have systole, which is when ventricles are contracting and pushing blood out, and between S2 and S1 of the next heart cycle, we have diastole which is when blood is filling the relaxed ventricles. Together, S1 and S2 form the “lub dub” of the heart beat.

Alright, now in addition to S1 and S2, there are two other "extra" sounds that are sometimes heard in the cardiac cycle, called S3 and S4. S3 and S4 are heard in different parts of diastole. In early diastole, which is right after S2, the atrioventricular valves are open and blood is flowing from the atria into the ventricles. If there’s a lot of blood coming in, the ventricles fill up quickly, and fluid waves bounce off of the walls of the ventricles which makes them vibrate, creating a third heart sound, or S3. S3 sounds kind of like “lub-dub-ta”. In trained athletes and also in pregnancy this is totally normal and just means that the ventricles are handling extra blood volume. But an S3 can also be a sign of volume overload, like in congestive heart failure, where there’s too much volume coming into the ventricles. Now, at the end of diastole, just before S1, the atria are contracting to get that last bit of blood into the ventricles. If the ventricles are stiff, meaning that they can’t easily relax, the atria will have to contract extra hard to push that blood in, creating the fourth heart sound, or S4. So, S4 sounds kind of like "ta-lub-dub". Oftentimes, this stiffness is because the ventricular muscles have hypertrophied, or increased in size, in order to pump against high blood pressure in the aorta or pulmonary artery. In other words, S4 is typically a sign of pressure overload, or severe hypertension.