cardiac cycle

Cardiac cycle

All the events associated with one heart beat is called Cardiac cycle.

Cardiac cycle includes contraction or systole of atria and ventricles and relaxation or diastole of atria and ventricles.

The Cardiac cycle includes all events associated with the blood flow through the Heart during one complete heart beat, I.e atrial systole and diastole followed by ventricular systole and diastole.

Stages of Cardiac Cycle

The normal number of Cardiac Cycle per-minute ranges from 60-80. If no. of Cardiac cycles per minute as 74, each cycle lasts for 0.8 seconds.

1. Atrial systole (0.1 sec)

In this stage, both atria contract forcing blood into ventricles.

Atrial systole is contraction of the Heart muscle of the left and right atria, both atria contract same time due to sino atrial node (SA node) wave of depolatozation.

2. Ventricular systole (0.3sec)

In ventricular systole both ventricles contract, forcing blood into Aorta and pulmonary trunk.

Ventricular systole is contraction of muscles of left and right ventricles, (QRS Complex in ECG).

3. Cardiac diastole(0.4sec)

Cardiac diastole is period of time when heart relaxes after contraction in preparation for refilling with circulating blood.

Ventricular diastole is when ventricle are relaxing, while artrial diastole is when atria are relaxing, together they are known as complete cardiac diastole.

1. Atrial diastole (0.7Sec)

Relaxation of atria.

VentRicle remain contracted and atria begin refilling with blood.

2. Ventricular Diastole (0.5sec)

Relaxation of ventricles.

It begins after atrial systole, allowing the ventricles to fill with blood.

When pressure in left ventricle drops below the pressure in left atrium, mitral valve opens, and left ventricle fills with blood from left atrium.

When pressure in right ventricle drops below that in the right atrium. Tricuspid valve opens, and right ventricle fill with blood from right atrium.

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