Assertion :- If all external nerve supplies to a human heart are cut there will be no effect on the heart beat.
Reason:- Human heart is a myogenic heart.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false.
D. If both assertion and reason are false

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that if all external nerve supplies to a human heart are cut, there will be no effect on the heartbeat.
- This is true because the heart has an intrinsic ability to beat independently of external nerve signals.

**Hint**: Consider how the heart functions without external input.

2. **Understanding the Reason**:
- The reason given is that the human heart is a myogenic heart.
- A myogenic heart means that the heart's contractions are initiated by the heart muscle cells (myocytes) themselves, rather than by nerve impulses.

**Hint**: Recall the definition of myogenic and how it relates to heart function.

3. **Connecting Assertion and Reason**:
- Since the human heart is myogenic, it can generate its own rhythmic contractions. Therefore, cutting external nerve supplies will not affect the heartbeat.
- This means the reason correctly explains why the assertion is true.

**Hint**: Think about how myogenic hearts function compared to neurogenic hearts.

4. **Evaluating the Options**:
- The first option states that both assertion and reason are true and the reason is the correct explanation of the assertion. This is the correct choice.
- The other options suggest that either one or both statements are false, which is incorrect based on our analysis.

**Hint**: Review the definitions and characteristics of myogenic vs. neurogenic hearts to reinforce your understanding.

### Final Answer:
The correct answer is the first option: Both assertion and reason are true, and the reason is the correct explanation of the assertion.