Final answer:
The QRS complex on an EKG indicates the depolarization of the ventricles, which is essential for their contraction to pump blood. This happens just before the increase in blood pressure during the systolic phase. The atrial repolarization also occurs during this time but is masked on the ECG.
Step-by-step explanation:
When the QRS complex is seen in an EKG, it represents the depolarization of the ventricles. This process occurs as the heart prepares for a strong contraction to pump blood to the lungs and the rest of the body. The QRS complex has a typical shape due to the complex shape of the heart and the path of the depolarization wave. This depolarization is vital for the ventricles to contract effectively, and it happens right before the surge of blood pressure seen in the systolic phase of the heartbeat. The ventricles begin to contract as the QRS reaches the peak of the R wave. Additionally, it is important to note that during the QRS complex, the repolarization of the atria also occurs, but it is not visible on the ECG as it is masked by the larger electrical activity of the ventricles.