Which phase of the ECG indicates ventricular excitation and contraction?

Options

A. P wave
B. QRS wave
C. T wave
D. XYZ wave

Answer

To determine which phase of the ECG indicates ventricular excitation and contraction, we can analyze the components of the ECG waveform:

1. **Understanding the ECG Waves**: The ECG consists of several key components: the P wave, the QRS complex, and the T wave. Each of these components corresponds to specific electrical activities in the heart.

2. **Identifying the P Wave**: The P wave represents the depolarization of the atria, which leads to atrial contraction. This phase does not involve the ventricles.

3. **Identifying the QRS Complex**: The QRS complex follows the P wave and is crucial for our question. It represents the depolarization of the ventricles, which leads to ventricular contraction. This is the phase where the ventricles are excited and contract to pump blood out of the heart.

4. **Identifying the T Wave**: The T wave occurs after the QRS complex and represents the repolarization of the ventricles. This phase indicates that the ventricles are recovering and preparing for the next cycle, but it does not indicate contraction.

5. **Conclusion**: Therefore, the phase of the ECG that indicates ventricular excitation and contraction is the **QRS complex**.

### Summary:
- The P wave indicates atrial contraction.
- The QRS complex indicates ventricular excitation and contraction.
- The T wave indicates ventricular repolarization.