What term means one heartbeat, or one contraction-relaxation cycle of the heart?

• A. Interval
• B. Cardiac cycle
• C. Holter monitor
• D. Depolarization

Answer: (B)

The cardiac cycle is the sequence of events that make up one heartbeat, from the start of one heartbeat to the start of the next. It includes the heart’s contraction (systole) to pump blood and its relaxation (diastole) to fill with blood, covering both atrial and ventricular phases in order. This whole cycle repeats with each beat, so it’s the term that means one contraction-relaxation cycle of the heart.

The other terms don’t describe the full repeatable sequence: an interval is just a span of time between two points within the cycle, a Holter monitor is a device for long-term ECG recording, and depolarization is the electrical change that triggers contraction rather than the entire cycle itself.