Cardiac Cycle

INTRODUCTION

Both electrical & mechanical events from beginning of one heart beat to beginning of next.

Duration of the cardiac cycle

Remember this!!!!!!

⇒ Normal heart rate à 75 beats / min
⇒ Duration of 1 beat = 60/75 = 0.8 sec
⇒ Blood flows from higher to lower pressure
⇒ Contraction increases the pressure while relaxation lowers the pressure
⇒ Valves open / close according to pressure gradients (AV valve open when atrial pressures are higher than ventricular pressures & close when pressure gradient is reversed. similarly semilunar valves open when ventricular pressures are higher than aortic/pulmonary pressure and close when it is reversed

So what is exactly happening???????

Duration of cycle	Events occurs	Heart sound	ECG relation
Atrial systole (0.11 secs)	Atria contracts ,blood enters ventricles via AV valves, semilunar valves closed	Inaudible 4rth heart sound is produced.	B/w P and Q wave.
Isometric contraction( 0.05 secs)	All the valves are closed. Raised pressure in the ventricles.	1st heart sound “LUBB “is heard due to the closure of AV valve.	Coincides with R wave of ECG
Ejection period (0.22 secs)	Ventricles contract, Semi lunar valves opens, blood is ejected into aorta & pulmonary arteries.
Protodiastole(0.04 secs)	Semilunar valves closed.	2nd heart sound “DUBB” is heard due to closure semilunar valves.	Appear after 0.09 secs after summit of T wave.
Isometric relaxation (0.06 secs)	All the valves are closed, pressure in the ventricles are reduced.
Rapid & slow filling (0.3 secs)	AV valves open, ventricles relaxes, filling occurs,	3rd heart sound is due to rapid filling & inaudible by stethoscope	b/w T and P wave