What phase is the heart in when it is at rest and filling with blood?

The heart is in the diastole phase when it is at rest and filling with blood. During diastole, the heart muscle relaxes, allowing the atria and ventricles to fill with blood from the body and lungs. This passive filling is crucial for ensuring that there is enough blood volume for the next contraction.

In this phase, the heart is not actively pumping blood out; instead, it is preparing for the next cycle of contraction known as systole. Consequently, understanding diastole is fundamental in comprehending the cardiac cycle and maintaining effective blood circulation.