Heart sounds and murmurs. (a) Normal heart sounds: once the ventricles start to contract at the onset of systole, the tricuspid and mitral valves close. Closure of the atrioventricular valves contributes to the rst heart sound which tends to be single. Aortic and pulmonary valves open soon after S1; however, this is usually inaudible in the normal heart. Flow across the aortic and pulmonary valves follows, which is again usually inaudible in the normal heart. The aortic valve closes rst, followed by the pulmonary valve; the delay in closure of the pulmonary valve gives the “split­ting” character of the second heart sound. Diastole, similar to systole is quiet; dur­ing diastole, blood ows through the tricuspid and mitral valves into the right and left ventricles. (b) Systolic ow murmur: increased blood ow across the pulmonary or aortic valve causes turbulence of blood ow which produces a systolic ow mur­mur heard over the left or right upper sternal border, respectively. In atrial septal defect, increased blood ow across the pulmonary valve causes a systolic ejection murmur along the left upper sternal border. Severe anemia with increase in blood volume to compensate for decreased oxygen-carrying capacity causes turbulence of blood ow and consequently a murmur across both aortic and pulmonary valves. These murmurs are distinguished from those caused by stenosis of the pulmonary or aortic valves by lack of a systolic ejection click heard just before the systolic murmurs. (c) Pulmonary or aortic valve stenosis: ow across the pulmonary and aortic valves occurs during midsystole; therefore, pulmonary or aortic stenosis produces a systolic ejection murmur preceded by a systolic ejection click. These murmurs are loudest over the right upper sternal borders in aortic stenosis and the left upper sternal border in pulmonary stenosis. The systolic ejection click is caused