Cardiac cycle:

A Heart beat completes in a sequence of three events:

• Auricular systole (contraction of auricles).
• Ventricular citole (Contraction of ventricles).
• Joint diastole (relaxation of both auricles & ventricles).

(1) During joint diastole, blood flows from veins (Superior vena cava & inferior vena cava) into both atrium and some blood passes to respective ventricles as respective valves are open. Here both are in relax posture.

(2) During auricular systole, auricles passes blood to their respective ventricles & starts relaxing & ventricles starts contracting.

(3) During ventricular systole, ventricles are fully contracted & passes blood to arteries. Now ventricles start relaxing and auricles are still relaxing. Again joint diastole starts. As it is the whole cycle restarts.

Cardiac output:

The volume of oxygenated blood pumped by left ventricles in body per minute is called cardiac output. Heart beats 72 times per minute and pump 70 ml blood in one beat.

Cardiac output per minute = 72 x 70 ml = 5040 ml

Heart sounds:

Heart produces two sounds – lub & dub during one beat.

Lub	Dub
(1) It is produced by closure of tricuspid & bicuspid valve. (2) Low pitched but of long duration. (3) It lasts for 0.15 seconds.	(1) It is produced by closure of semi lunar valves. (2) High pitched but of short duration. (3) It lasts for 0.1 seconds.