What phase of the heart cycle is characterized by muscle relaxation?

The phase of the heart cycle characterized by muscle relaxation is diastole. During diastole, the heart muscle relaxes, allowing the chambers to fill with blood. This period is crucial for supplying the heart and the rest of the body with oxygenated blood. In this phase, both the atria and ventricles undergo relaxation, the atrioventricular valves are open, and blood flows into the heart from the veins.

Systole, in contrast, is the phase when the heart muscle contracts to pump blood out of the heart. Atrial contraction occurs during a part of diastole but is specifically about the atrial muscles contracting to push blood into the ventricles. Ventricular contraction refers to the systole phase of the ventricular muscle where blood is pumped into the aorta and pulmonary artery. Understanding these phases is fundamental when analyzing electrocardiograms and the overall function of the cardiovascular system.