The rhythmic contraction and expansion of the heart together is called the heart beat. An adult’s heart beats 70-80 times per minute (average 75 times). Sympathetic nerves and the hormones adrenaline and thyroxine increase the heart rate. Parasympathetic nerves decrease heart rate. There are two types of heart beats. –
1. Lab: At the beginning of systole, the sound made when the atrioventricular valves (bicuspid and tricuspid) close is called lab.
2. Dub: The sound made when the semilunar valves close at the end of systole is called Dub.