During atrial contraction, what percentage of blood enters the ventricles?

During atrial contraction, approximately 30% of the total ventricular filling occurs. This phase is known as "atrial systole," and it plays a crucial role in completing the filling of the ventricles before they contract.

In a typical cardiac cycle, most of the blood enters the ventricles passively during diastole due to the pressure difference between the atria and ventricles. However, atrial contraction adds a significant amount of blood, ensuring the ventricles are optimally filled before the next ventricular contraction.

This coordinated action is vital for maintaining adequate stroke volume and overall cardiac output. Understanding this percentage helps to highlight the importance of atrial function and its impact on heart efficiency and hemodynamics.