Absolute refractory period of heart is during

Options

A. contraction when the heart is in non responding period
B. expansion
C. negative charge
D. positive charge

Answer

To answer the question regarding the absolute refractory period of the heart, we will break down the concept step by step.

### Step-by-Step Solution:

1. **Understanding Refractory Periods**: The refractory period is a phase during which the heart muscle cannot respond to further stimulation. It is crucial for the proper functioning of the heart, ensuring that it has time to contract and relax.

2. **Types of Refractory Periods**: There are two types of refractory periods in cardiac muscle:
- **Absolute Refractory Period**: This is the phase during which no new action potential can be initiated, regardless of the strength of the stimulus. This occurs because the sodium channels are inactivated.
- **Relative Refractory Period**: This follows the absolute refractory period, where a stronger-than-normal stimulus can initiate an action potential.

3. **Duration of the Absolute Refractory Period**: The absolute refractory period in cardiac contractile muscle lasts approximately 200 milliseconds. This is essential for preventing tetanus (sustained contraction) in the heart muscle.

4. **Timing of the Absolute Refractory Period**: The absolute refractory period coincides with the contraction phase of the heart (systole). During this time, the heart is not able to respond to any new electrical impulses.

5. **Conclusion**: Therefore, the absolute refractory period of the heart occurs during the contraction phase when the heart muscle is not responsive to further stimulation.

### Final Answer:
The absolute refractory period of the heart is during contraction.

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