What is the term for the phase when the heart muscle is relaxing?

The phase when the heart muscle is relaxing is called diastole. During diastole, the heart chambers—specifically the atria and ventricles—are filling with blood from the circulation. This relaxation occurs after the heart muscle has contracted to pump blood out of the chambers, a phase known as systole. Diastole is critical for allowing the heart to refill with blood, ensuring adequate blood supply to the body. Understanding this phase is essential for interpreting EKG readings since the heart’s electrical activity corresponds to these mechanical processes. Effective filling during diastole contributes to the efficiency of the heart's pumping function.