 Welcome to the electrocardiogram. This learning object relates the cardiac cycle to an electrocardiogram. The electrocardiogram, or ECG, measures electrical impulses across the heart. The various waves of the ECG represent different stages of the cardiac cycle. The P wave represents atrial depolarization. Repolarization occurs just prior to contraction or systole. The QRS complex represents ventricular depolarization. Depolarization occurs just prior to contraction or systole. The T wave represents ventricular repolarization. Repolarization occurs just prior to relaxation or diastole. Now see if you can answer the following three questions about the electrocardiogram. Congratulations! You've completed the electrocardiogram.