What does the QRS complex represent in the cardiac cycle?

The QRS complex represents ventricular depolarization in the cardiac cycle. This is a critical phase in the heart's electrical activity. During ventricular depolarization, the electrical signals move through the ventricles, causing them to contract and pump blood out of the heart. This is visually represented on the electrocardiogram (ECG) as the QRS complex, which typically appears as a sharp spike followed by a downward deflection before returning to the baseline.

This complex is essential for effective cardiac function because it indicates that the ventricles are responding to the signals received from the atria through the AV node down the bundle of His and into the Purkinje fibers. The proper functioning of this process is vital for maintaining an efficient heart rhythm and responding to the body’s demands for oxygenated blood.

The other options do not accurately describe the QRS complex. Atrial depolarization occurs during a different segment of the ECG known as the P wave, and atrial contraction follows that depolarization but is not represented by the QRS complex. Similarly, ventricular repolarization is captured by the T wave, not the QRS complex. Understanding these distinctions is key in interpreting ECG readings and recognizing heart function accurately.