The P waves in an electrocardiogram (ECG or EKG) represent the electrical impulse that causes the atria (the upper chambers of the heart) to contract and pump blood into the ventricles (the lower chambers of the heart). Each P wave is followed by a QRS complex, which represents the electrical impulse causing the ventricles to contract. The P waves can provide information about the heart rate, the regularity of the heartbeat, and the presence of any abnormalities in the electrical conduction of the heart.