Phase 2 - Isovolumetric Contraction

The second stage of the cycle relates directly to the QRS complex. Ventricular depolarisation causes the following:

• Excitation-contraction coupling  (ECC) –  The process of an action potential causes a myocyte to contract.
• Myocyte contraction
• Rapid increase in intraventricular pressure

Atrioventricular valves close as soon as intraventricular pressure is greater than atrial pressure.  The atria then repolarise whilst remaining in diastole.

Heart Sounds:

First Heart sound, S1, produced by the left ventricle, can be heard due to turbulence in blood surging against closed AV valves and impact of the heart against chest wall.

Did you know..?

   Its called ‘Isovolumetric’ because ventricles contract but do not eject blood yet as there is no change in their volume. This is because the pressures in the aorta (80 mmHg) and pulmonary trunk (10 mmHg) are still greater than respective ventricles opposing the opening in semilunar valves.