The cardiac cycle is a single cycle of filling and emptying of the heart. Diastole is the time when the heart is relaxed and the chambers are filling with blood. Systole is the time when the heart is contracting and pumping blood. Contraction causes a rise in pressure in blood vessels that is felt as a pulse in surface arteries. The heart beats about 70 times per minute.
Heart sounds are due to turbulence on the closing of valves during the cardiac cycle. The first heart sound (S1, lub) is heard when the AV valves close as the ventricles start to contract (the beginning of systole). The second heart sound (S2, dub) is heard when the semilunar valves as the ventricles relax (the beginning of diastole).
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