In what situation would the heart muscle be in systole?

The heart muscle is in systole during the phase when it contracts to pump blood out of the chambers of the heart. This contraction occurs primarily in the ventricles and is necessary to propel blood into the pulmonary artery and aorta, supplying the lungs and the rest of the body with oxygenated blood.

During this phase, the pressure within the ventricles rises significantly, leading to the closure of the atrioventricular valves (to prevent backflow into the atria) and the opening of the semilunar valves, which allow blood to exit the heart. This process is fundamental to the cardiovascular system, as it ensures that oxygen-rich blood reaches the body and that deoxygenated blood is sent to the lungs for reoxygenation.

In contrast, the other scenarios describe diastole, which is when the heart muscle relaxes and fills with blood, the heart is at rest, or when heart valves close during the transition between the two phases.