When does the QRS complex occur in relation to heart activity?

The QRS complex represents the electrical depolarization of the ventricles, which corresponds to the contraction of the ventricles. During this phase, the heart's electrical activity is triggered in the bundle of His and spreads through the Purkinje fibers, leading to ventricular contraction (systole). This contraction is crucial because it propels blood out of the heart to the lungs and the rest of the body.

Understanding the timing of the QRS complex is essential in interpreting EKGs, as it provides insights into the heart's rhythm and function. In contrast, atrial contraction occurs earlier and is represented by the P wave, while heart relaxation is indicated by the T wave, which occurs after the QRS complex. Thus, noting that the QRS complex is aligned with ventricular contraction is key to understanding the mechanics of the heart during the cardiac cycle.