The four cardiac valves are classified into two types - the atrioventricular [mitral and tricuspid] and the semilunar [aortic and pulmonic] valves. This is an important distinction. During systole, atrioventricular valves are closed and semilunar valves are open.
In diastole the opposite is true. Atrioventricular valves are open to allow ventricular filling and semilunar valves are closed to prevent backflow of blood to the heart from either systemic circulation or pulmonary circulation.
Because atrioventricular and semilunar valves function oppositely in the cardiac cycle the effects of stenosis and insufficiency are different. Stenosis of the semilunar valves causes systolic murmurs: aortic stenosis(AS) and pulmonic stenosis(PS). Stenosis of the atrioventricular valves causes diastolic murmurs: mitral stenosis(MS) and tricuspid stenosis(TS). Insufficiency of the semilunar valves is associated with diastolic murmurs: aortic insufficiency(AI) and pulmonic insufficiency(PI). Insufficiency of the atrioventricular valves causes systolic murmurs: mitral regurgitation(MR) and tricuspid regurgitation(TR).
There are four important areas used for listening to heart sounds. These are: Aortic area, Pulmonic area, Tricuspid area, Mitral Area (Apex).
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