What is the duration a cardiac cycle is defined as?

The duration of a cardiac cycle is defined as the time from the beginning of one heartbeat to the beginning of the next. This definition encompasses the entire sequence of events in the heart, including the phases of contraction (systole) and relaxation (diastole).

By measuring this duration, we are able to understand the heart's overall functioning and rhythm, which is crucial for diagnosing various cardiovascular conditions. The cardiac cycle includes all the electrical and mechanical activities that occur between consecutive heartbeats, providing a comprehensive overview of the heart's performance over time.

The other choice describing the time between two heartbeats might seem similar but lacks the precision of specifying "from the beginning of one heartbeat to the beginning of the next." Choosing the term that captures the complete cycle's start and end ensures clarity and accuracy in understanding cardiac physiology. The focus on atrial contraction or the heart’s resting phase does not encompass the full cycle’s rhythmical activities and is thus not an appropriate definition for the duration of a cardiac cycle.