Correct Option
The correct option is 0.8 s.
Explanation
The cardiac cycle represents the sequential pattern of contraction (systole) and relaxation (diastole) of the heart chambers during a single heartbeat. The duration of this cycle is inversely proportional to the heart rate.
Detailed Analysis
In a healthy, resting human adult, the heart typically beats approximately 72 times per minute. The duration of a single cardiac cycle is calculated by dividing the total time in a minute by the number of beats.
- Calculation: 60 seconds / 72 beats ≈ 0.8 seconds.
This 0.8-second duration is distributed among the different phases of the cardiac cycle as follows:
- Atrial Systole: Approximately 0.1 seconds (atria contract).
- Ventricular Systole: Approximately 0.3 seconds (ventricles contract).
- Joint Diastole: Approximately 0.4 seconds (all chambers are in a relaxed state).
Consequently, the total time for one complete cycle of contraction and relaxation is 0.8 seconds.
Key Takeaway: The duration of a cardiac cycle in a resting adult is 0.8 seconds, corresponding to an average heart rate of 72 beats per minute.