What is Cardiac cycle

Cardiac cycle is the sequence of event in one heartbeat which consist of one systole and diastole

sequence of event is atrial systole, ventricular systole , ventricular diastole and atrial diastole

During atrial systole, excitatory of electrical impulses which generated in the sinoatrial node (SA node) spread to the both the right and left atria

This causes the atria to contract

The  contraction causes the pressure to increase in both the atria

AV valve open

This will allow the blood to flow from the atria to the ventricles

During ventricles systole , excitatory impulse move to atrioventricular node (AV node) down the Bundle of His and Purkinje fibre to the ventricular muscles

The ventricular muscle contracts (ventricular systole)

The blood pressure inside the ventricles increased

AV valve closed wben ventricular pressure is higher than atrial pressure

 The closing of AV valve produced the first heart sound 'lub'

The ventricular pressure rises and exceeds in the aorta and pulmonary artery

This cause the semilunar valves open

This allows the blood to flow from left ventricle to aorta and from right ventricles to pulmonary artery

During ventricular diastole , ventricles relax

Pressure in ventricle is lower than the pressure inaorta and pulmonary artery

Blood in the arteries start to flow backwards into the cups of semilunar valves

this will close the semilunar valves and produced the second heart sound 'dub'

As the ventricles xontinues to relax , the ventricular pressure falls rapidly 

When ventricular pressure less than atrial pressure , the AV valve are forced to open

During atrial diastole, atrial will relax and the right atria receives deoxygenated blood from the body tissues to vena cava

Left atria received oxygenated blood from the lung to pulmomary vein