As a cardiac electrophysiologist, I specialize in the study of the electrical activity of the heart. The P wave, QRS complex, and T wave are fundamental components of an electrocardiogram (ECG or EKG), which is a graphical representation of the heart's electrical activity over time. The P wave represents the depolarization of the atria, which is the process by which the atria contract to push blood into the ventricles. This wave is typically small and can sometimes be difficult to see, especially in individuals with certain heart conditions. The QRS complex is a larger, more prominent wave that signifies the depolarization of the ventricles. This is a critical phase where the ventricles contract to pump blood out to the body. The Q wave is the first negative deflection, the R wave is the first positive deflection, and the S wave is the subsequent negative deflection following the R wave. Following the QRS complex, the T wave represents the repolarization of the ventricles, which is the process by which the ventricles return to their resting state after contraction. This is important for the heart's preparation for the next beat. In summary, the ECG's P wave, QRS complex, and T wave correspond to the atrial depolarization, ventricular depolarization, and ventricular repolarization, respectively. read more >>

Atrial and ventricular depolarization and repolarization are represented on the ECG as a series of waves: the P wave followed by the QRS complex and the T wave. The first deflection is the P wave associated with right and left atrial depolarization. ... The first positive deflection in the complex is called an R wave.read more >>