The electrocardiogram is a report generated depicting the electrical activities of the heart. It resembles a graph paper showing time in secs on the X axis and current in millivolt on the Y axis. The wave 1 is the P wave which indicates the current generated from the SA node going towards both the atria and the AV node. The P wave represents the electrical activity - atrial depolarization and the segment PQ indicates the muscular activity of atrial contraction. The waves 2, 3 & 4 are called the Q,R,S waves which represent the electrical activity - ventricular depolarization indicating that the current moves from the AV Node to the Bundle of His to the Purkinje fibers. The ST segment after that represents the muscular activity of ventricular contraction. The wave 5 is the 'T' wave which represents the electrical activity - ventricular repolarization. The segment after that indicates the muscular activity of ventricular relaxation.