What are the primary phases of the cardiac cycle?

The primary phases of the cardiac cycle are indeed diastole and systole, which refer to the two main states of the heart function during each heartbeat. Diastole is the phase when the heart muscle relaxes, allowing the chambers to fill with blood. During this phase, both the atria and ventricles are relaxed, and blood flows into the heart from the body and lungs.

Systole, on the other hand, is the phase when the heart muscle contracts, pumping blood out of the chambers. In this phase, the ventricles contract to eject blood into the arteries—specifically, the right ventricle pumps blood to the lungs via the pulmonary artery, while the left ventricle pumps blood to the rest of the body through the aorta.

Choosing diastole and systole highlights the overarching functional states of the heart, making it a more complete representation compared to options that focus on specific parts of the cycle, such as atrial or ventricular activities. This distinction is crucial in understanding the overall mechanics of the heart during each cycle, emphasizing the alternating states that are essential for effective blood circulation.