Which part of the ECG reflects the electrical activity leading to ventricular contraction?

The QRS complex is fundamental in the ECG as it represents the electrical depolarization of the ventricles, which directly leads to ventricular contraction. During the QRS complex, the electrical impulses travel through the ventricles, causing them to contract and pump blood to the lungs and the rest of the body. This phase is crucial for maintaining circulation and facilitating the delivery of oxygen and nutrients.

The other components, such as the P wave, represent atrial depolarization, which occurs before the ventricles contract. The ST segment reflects the period between ventricular depolarization and repolarization, while the T wave indicates the repolarization of the ventricles after contraction. Each of these components plays an important role in the cardiac cycle, but it is the QRS complex that specifically marks the moment of ventricular contraction.