What is the difference between systole and diastole?

Systole and diastole are fundamental phases of the cardiac cycle, which describes the actions of the heart during one complete heartbeat.

Systole refers to the phase when the heart muscles contract. During this time, the ventricles contract to pump blood out of the heart: the right ventricle sends blood to the lungs for oxygenation, while the left ventricle pumps oxygenated blood to the rest of the body. This phase is crucial for maintaining circulation and ensuring that all body tissues receive the oxygenated blood they require.

Diastole, on the other hand, is the phase of relaxation. During diastole, the heart muscle relaxes, allowing the chambers (atria and ventricles) to fill with blood from the body and lungs. This filling phase is essential because it prepares the heart for the next contraction, ensuring that there is adequate blood volume ready to be pumped out during systole.

The distinction between these two phases is vital for understanding heart function and the overall efficiency of the cardiovascular system. Recognizing that systole is associated with contraction and blood ejection, while diastole involves relaxation and filling, is fundamental to many clinical assessments, including blood pressure measurements which are expressed in terms related to these phases.