It seems that the most common pathologic sign in cardiac auscultation is fourth heart sound S4. When I was learning heart auscultation many years ago, it was hard to me to understand and hear S4 because of its close proximity to first heart sound S1.
S4 corresponds to atrial contraction. It is probably always abnormal sign. You could imagine sequence S4-S1 like stairs with two steps: the first step is S4, the second one is S1. S4 is a lower step and S1 is an upper one. S4 consists of low frequencies only, S1 contains low and high frequencies. Imagine stairs with two steps when you hear S4.
Very frequently Acute MI is associated with loud S4. Here is an example. Use headphones for better hearing.
S4 is a sign of many diseases such as AH, CAD, etc. In simple words, S4 is a sign of diseased heart. In other words, when you hear S4 you can not say, that the heart of your patient is healthy. S4 alone is not sufficient for precise diagnosis. S4 says that this heart is not healthy. That is all.
