The human heart is a complex machine, with many parts pushing and pulling, and blood continuously flowing through the heart and great vessels. All of this commotion can be heard, and yields valuable information to the trained ear. In a healthy heart, the only noticeable sounds are those of the valves closing. Various heart disease affect these sounds in different ways, which is what makes this a valuable diagnostic technique.
Many people have slight abnormalities of their heart or great vessels which yield unusual sounds, but they're perfectly healthy. Thus, there's no single normal complex of heart sounds. But there is a minimal complex, which is the widely-imitated "lub-dub", two-beat sound. In medical parlance, these two sounds are S1 and S2. Both of these sounds can be broken down further.
The first sound, S1, is generated by the closing of the mitral (M1) and tricuspid (T1) valves. Usually the closure of the tricuspid follows so closely on the mitral closure that they're perceived as a single sound. The second sound, S2, is composed of the aortic (A2) and pulmonic (P2) valve closures.
Although the aortice and pulomnic closures are frequently very close together, the A2-P2 interval widens when breathing in. If you listen closely to the following sound, you'll hear an occassional stutter in the pattern. The "stutter" is the widening of the interval, so that A2 and P2 are perceived distinctly.
In mitral stenosis the mitral valve leaflets thicken, causing
increased flow across the mitral valve. This turbulent flow through
the valve is heard as the characteristic murmur of
mitral stenosis. A frequent cause of mitral stenosis is rheumatic
fever, which causes scarring of the valve leaflets, thickening them.
Below, a single frame from an echocardiogram illustrates the
thickening of mitral stenosis.
Mitral stenosis is occassionally accompanied by mitral regurgitation. The regurgitation results when the valve leaflets fail to close properly, and allow blood to flow back through the mitral valve. Together, these produce a cacophony of sounds.