What does the QRS complex represent in an ECG?

The QRS complex in an ECG represents ventricular depolarization leading to ventricular contraction. This phase of the cardiac cycle occurs when the electrical impulses spread through the ventricles, causing them to contract and pump blood out to the lungs and the rest of the body.

During the QRS complex, which consists of three deflections (the Q wave, R wave, and S wave), the ventricular myocardium is activated. This electrical activity is crucial for coordinating the heart's pumping action.

In contrast, the other options refer to different phases or events within the cardiac cycle. The first option mistakenly links the QRS complex to heart relaxation instead of contraction. The third option addresses atrial depolarization, which is represented by the P wave, not the QRS complex. Finally, the fourth option incorrectly attributes the QRS complex to ventricular repolarization; this process actually corresponds to the T wave on the ECG, which indicates recovery and relaxation of the ventricles after contraction. Understanding the specific role of the QRS complex is essential for interpreting ECGs accurately and recognizing normal versus abnormal heart rhythms.