What comprises the cardiac cycle?

The cardiac cycle consists of the complete sequence of events in one heartbeat, which includes the contraction and relaxation phases of all four chambers of the heart. This is accurately described by including both systole and diastole phases for the atria and ventricles.

Systole refers to the phase when the heart muscles contract, leading to the ejection of blood from the chambers, while diastole is the relaxation phase, during which the chambers fill with blood. Together, these actions ensure efficient circulation throughout the body. By encompassing all phases of the cardiac cycle, including those of both atria and ventricles, you gain a comprehensive understanding of how the heart operates during a complete heartbeat.

In contrast, the other options do not adequately cover the full scope of the cardiac cycle:

• A focuses on just resting and active phases, which oversimplifies the process.

• C describes only a partial aspect of the cycle by mentioning atrial contraction and ventricular relaxation, without addressing all phases.

• D emphasizes the sequential contraction of the left and right atria, which does not encompass the full cardiac cycle including ventricular actions.

Thus, the most accurate depiction of the cardiac cycle is the inclusion of both systole and diastole for all heart chambers