The Human Heart

Although you may not have been able to tell until right now, I am a Nursing Student, and this will be a nursing post, cheifly about heart function and murmers =). I'm not going to explain in depth how the thing works, but the basic idea is that blood comes into the heart from the Superior and Inferior vena cavea, which join and empty into the right atrium. From the right atrium, the unoxygenated blood is pumped into the left ventrical (which, incidentally, covers most of the front of the heart) and out into the pulmonary artery which travels to the lungs. The oxygenated blood travels back to the heart via the pulmonary vein and into the Left Atrium, from there to the left ventricle, and is then pumped into the aotra. The diagragm below is a little on the crummy side (I don't like the aspect ratios) but I couldn't find a better one. Besides, it's labeled =).

There are numerous heart dysrhythmias and dysfunctions, but I'm going to focus only the actual dysfunctions and such and not the conditions they are typical of.
A normal heart sounds sort of like saying "lub dub (pause) lub Dub, etc." Lub is the first heart sound and is termed S1. Dub is the second heart sound and is termed S2.

The first heart sound is denoted as S1, and is caused by the closure of the atrioventricular valves. A split milli-second after their closure, the semilunar valves (those going from the ventricle into the pulmonary artery and the aorta) open and blood rushes out of both chambers. Meanwhile, the atria are filling from the vena cava and the pulmonary vein. The period of atrial filling/ventricular emptying is the period known as systole, the space between the first and second heart sound.

On S2, the sound is caused by the closure of the semilunar valves (the tricuspid and aortic). This begins the period of diastole. Shortly after their closure, the atrioventricular valves open, and the ventricles are filled as the blood is pumped into them from the atria. The valves shut and S1 begins all over again.

In children and young adults, an S3 sound may be heard during diastole, shortly after S2. It is caused by a rapid deceleration of the column of blood against the ventricular wall. In older adults, it usually indicates a pathological change in ventricular compliance. When auscultated with a stethoscope, it sounds like "Kentucky."

An S4 sound is not often heard in normal adults, and marks atrial contraction. It comes right before the S1 sound, and also indicates a pathological change in ventricular contraction. It sounds as if one were saying "Tennessee."

Normally, S1 and S2 are a single sound, but they may be split due to the two valves which are supposed to be closing on that sound not closing together. A split S2, in my experience anyhow, is rather common and usually not pathological (that is, not a case for worry). It often occurs in healthy young adults on inspiration (breathing in) and goes away on expiration (as my sister said, everything goes away when you die, doesn't it ;-P). S1 spilt is an earlier mitral sound and a later tricuspid sound, with the mitral being lounder. This is heard best at the lower the lower left sternal boarder (for those of you who care ;-)), does not vary with respiration, and is often pathological.

Heart murmurs (my old freinds) are caused either by stenosis--a sluggish opening of a valve (blood is flowing through before the valve is completely open, causing turbulance)--or by regurgitation, with blood flowing back into the chamber it has just exited because the valve closed slowly/incompltely. Murmurs, however, are extremely interesting and must have their own post, at a later date.