ABSTRACT
The first part of the double-sound (1st heart sound, S-l) is the rebound of blood against the heart wall after contraction of the ventricles (systole) and closure of the atrioventricular valves (AV valves-mitral and tricuspid). The second part of the double-sound (2nd heart sound, S-2) is the back-recoil of blood against the closed semilunar valves-pulmonary and aortic-so-called because they are half-moon shaped). The two sounds are magnified by the stethoscope as “lub-dup”. In the adult, the average heart rate is about 70 beats per minute. The range is 60 to 100, with exceptions. Below 60 is brady cardia; above 100 is tachycardia. The heart rate or pulse is measured by count ing the number of beats for 15 seconds and multiplying by four. If an arrhythmia is suspected, the number of beats is counted for one minute (Fig. 3.1).
