Which of the following statements is correct ?

Options

A. The T-wave in an ECG represent excitation of ventricles
B. The sum of P and T waves in a given time period can determine the heart beat rate of an individual
C. The end of the P-wave marks the end of the systole
D. In a standard ECG, a person is connected to the machine with three electrical leads.

Explanation

To determine the correct statement regarding the ECG (electrocardiogram), we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the T Wave in ECG:**
- The T wave in an ECG represents the relaxation phase of the ventricles, known as ventricular diastole, not excitation. Therefore, the statement "The T wave in an ECG represents excitation of ventricles" is incorrect.

2. **Heartbeat Rate Determination:**
- The heartbeat rate is primarily determined by the QRS complex, which represents the contraction of the ventricles (ventricular systole). The statement "The sum of P and T waves in a given time period can determine the heartbeat rate of an individual" is incorrect because the P and T waves do not directly correlate with the heartbeat rate.

3. **End of P Wave and Systole:**
- The P wave represents the contraction of the atria (auricular systole). The end of the P wave indeed marks the end of the atrial contraction (systole). Therefore, the statement "The end of the P wave marks the end of the systole" is correct.

4. **Number of Leads in ECG:**
- In a standard ECG, typically 12 electrodes (leads) are used to measure the electrical activity of the heart, not just three. Therefore, the statement "In an ECG, a person is connected to a machine with 3 electrical leads" is incorrect.

### Conclusion:
The correct statement among the options is: **"The end of the P wave marks the end of the systole."**

---