Cardiac cycle is a part of cardiovascular system. The cardiovascular system is transport system it transport nutrition to tissue ,WBC to tissue, antibodies to tissue.
The cardiac cycle is the performance of the human heart from the beginning of one heart beat to the beginning of the next.

cardiac cycle

Periods of heart beat

• It consists of two periods that is the systole and diastole.
• And these two periods are formed by two events – systole and diastole.
• Each Heartbeat consists of two major periods systole and diastole during systole heart contract and from the blood through our tree during diastole heart relax and blood is filled in the heart.
• All these changes are repeated during every heart beat in a cyclic manner.


• The arterial events.
• The ventricular events.
Atrial events is also consists of two periods that are atrial systole and Atrial diastole.
• In the same way ventricular events also consists of two periods that are ventricular systole and ventricular diastole.


  • Atrial contraction.
  • Isovolumetric contraction.
  • Rapid ejection phase.
  • Slow ventricular ejection phase.
  • Protodiastole.
  • Isovolumetric relaxation.
  • Rapid ventricular filling phase
  • Slow ventricular filling phase.

Atrial Contraction

  • This is the first phase of cardiac cycle in which there is contraction of atria and 80% of ventricle filling is already done.
  • Atrial contraction contributes only last 20% of ventricle feeling/active filling.
  • Atrioventricular and mitral Valves are open.
  • Aortic and pulmonary Valves are closed.
  • A-wave is produced indicating increase in pressure in atria due to contraction.

Isovolumetric contraction

Isovolumetric contraction means the size and the shape of the heart muscle is same but the volume increase and the pressure increase in the ventricle.
Ventricle start to contract and pressure reached upto 80 mm of HG.
Mitral and Atrioventricular Valves are closes which produce first heart sound/S1.
C-wave is produced back pressure in atria.
V-wave due to accumulation of blood coming from lungs to atria.
Aortic and pulmonary valve remain closed.

Rapid ejection phase

Blood is fastly goes to the pulmonary trunk and aorta.
Aortic and pulmonary valves open and blood rapidly pumped into aorta and pulmonary trunk.
Pressure and contraction still continues atria act as a reservoir and gathering the blood from lungs and right atria collect blood from superior and inferior vena cava.

Slow ventricular ejection and Protodiastole phase

Slow ventricular ejection phase–  In which the atria filling continuous and pressure start falling in ventricles. Aorta and pulmonary trunk still receiving blood from ventricles.

Protodiastole phase – the first stage of  relaxation.

Isovolumetric relaxation-

S2/second heart sound is produced due to closure of aortic and pulmonary valve.
This phase both atrioventricular and pulmonary valves are closed and ventricles start to relax which leads to fall in pressure of ventricles.
After the ejection phase all valves are closed and the volume of blood left in ventricle is known as end systolic volume i.e. 70 to 80 ml blood is left.


Rapid filling phase-

Pressure becomes less than the pressure in atria and mitral/Atrioventricular valves open.
Passive filling of ventricle occurs without atrial contraction up to 80% ventricle filled.
Aortic and pulmonary valves still closed.
Sometimes S3 is produced during exercise.

Slow filling phase

In this phase ventricles directly receive blood from atria through atrium.
Aortic and pulmonary valves still closed and mitral/AV valve open.
In hypertrophied ventricle when atria contract sometimes produce a sound S4/4th heart sound.  This is usually pathological.

Significance of cardiac cycle

1.Helps in determining rate and rhythm sound of heart.
2.Determination of heart sound
3.For determining duration and timing of murmurs sound.

            Pathophysiology of cardiac cycle

Cardiac cycle is altered in some conditions like in cardiac failure myocardial infarction,  arrhythmia, valve incompetency and vascular diseases.