Which phases are included in the cardiac cycle?

The cardiac cycle consists of a sequence of events that occur during one complete heartbeat, and it primarily includes the phases of contraction (systole) and relaxation (diastole). During systole, the heart muscle contracts to pump blood out of the chambers, effectively filling the arteries, while during diastole, the heart muscle relaxes, allowing the chambers to fill with blood from the atria and venous system.

Focusing on contraction, the myocardial fibers shorten and generate pressure within the ventricles, leading to the ejection of blood into the aorta and pulmonary artery. In contrast, the relaxation phase allows the heart chambers to expand and refill, which is crucial for maintaining adequate blood flow and pressure.

While other phases like filling and emptying occur as part of these broader processes, the specific terms "contraction" and "relaxation" directly convey the mechanical actions of the heart that define the functional aspects of the cardiac cycle. Therefore, the phases that emphasize the heart's action during a complete cycle are accurately described as contraction and relaxation.