Question

In normal condition, duration of cardiac cycle is

• A. 2.0 sec
• B. 0.8 sec
• C. 0.2 sec
• D. 1.5 sec

Hint:

If an animal's heart rate increases, the overall duration of the cardiac cycle decreases, with the diastole (relaxation) phase showing the greatest reduction.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The cardiac cycle comprises all the mechanical and electrical events that occur from the beginning of one heartbeat to the beginning of the next.

Step 2: Key Formula or Approach:
The duration of a single cardiac cycle is inversely proportional to the heart rate (HR) and can be calculated using the relation:
\[ \text{Cardiac Cycle Duration} = \frac{60}{\text{Heart Rate (bpm)}} \]

Step 3: Detailed Explanation:
Assuming a standard resting mammalian heart rate of approximately \(75 \text{ beats per minute (bpm)}\):
\[ \text{Cardiac Cycle Duration} = \frac{60}{75} = 0.8 \text{ seconds} \]
This \(0.8\text{-second}\) interval is divided into:
- Atrial systole: \(0.1\text{ s}\)
- Ventricular systole: \(0.3\text{ s}\)
- Complete cardiac diastole (joint diastole): \(0.4\text{ s}\)

Step 4: Final Answer
The standard duration of a cardiac cycle in normal resting conditions is 0.8 seconds.