Devin Nickol, M.D.
1. This is a recording of a normal heart. Listen carefully to distinguish S1 and S2. Note that the period of time between S1 and S2 (systole) is shorter than the period of time between S2 and the next S1 (diastole). This is helpful in distinguishing systolic from diastolic murmurs. Unfortunately, in a tachycardic patient diastole shortens and is often more difficult to distinguish from systole. It may help to remember that S1 is usually louder than S2. In any case, whenever you listen to heart sounds you should first try to clearly identify S1 and S2 in order to "get your bearings".
2. Here the mitral and tricuspid components of S1 have become separated enough to be distinguished as two separate sounds. The result is a split S1. This can be difficult to distinguish from an S4 (see below).
3. In this case, the aortic and pulmonic components of S2 have become separated enough to be distinguished as two separate sounds. This happens normally during inspiration, and in that case it is referred to as a "physiologically split" S2. An S2 that remains split during both inspiration and expiration is referred to as a "fixed split" S2.
4. In addition to the "normal" components of the cardiac cycle (S1 and S2), occasionally "extra" sounds will be present. These are named according to their location in the cardiac cycle, and the nature of the sound they make. An S3 is a sound occuring shortly after S2 (makes sense....), and can be difficult to distinguish from a split S2. In most cases, an S3 will occur later than the second component of a split S2, which can be helpful in telling them apart. Compare this recording to the recording of the split S2 above. Hear the difference?
5. While an S3 is located shortly after S2, an S4 occurs later in the cardiac cycle. So much later, in fact, that it occurs shortly before the next S1. Distinguishing an S3 from an S4 can be challenging. The rhythm of the sounds may be helpful - since an S3 occurs close to S2, the cardiac cycle sounds something like the word "Kentucky", with the last two syllables coming in rapid succession. Try saying it a few times out loud to get the feeling. Ignore those people staring at you....they're just in awe of your rapidly developing auscultation skills. An S4, on the other hand, makes the cardiac cycle sound more like the word "Tennessee", with the first two sounds occurring close together. In a tachycardic patient with both an S3 and S4, diastole may shorten enough to cause a "summation gallop" - the S3 and S4 fuse to form one sound.
6. In addition to the sounds we've discussed so far, there are several other "extra" sounds that may wind up in the cardiac cycle for various reasons. These include clicks (often as a result of abnormalities in valve movement), rubs (perhaps from irritation of the pericardium), and even "plops" (such as from an atrial myxoma flopping around). Mitral valve prolapse is a common condition which may produce systolic clicks and/or murmurs. The first recording below demonstrates a late systolic click with no murmur. Listen until you are convinced that the click occurs before S2. Realize that the very first sound you hear in this recording is actually an S2 - as mentioned above, it's always a good idea to spend several seconds just listening to S1 and S2 until you are sure you know which is which. The second recording below demonstrates a mid-systolic click followed by a murmur that continues through the rest of systole. It is difficult to distinguish the click from the beginning of the murmur.
7. Many people find diastolic murmurs more difficult to hear than systolic murmurs. This may be due to the fact that they are often low pitched, and therefore it is important to always listen with both the diaphragm and bell. Below is a recording of a murmur which starts immediately following S2, continues through most of diastole, but clearly ends before the next S1. The murmur actually obscures S2 almost completely. Remember to identify S1 and S2 when you first begin listening.