Abstract 1. 1. The U wave of the human electrocardiogram is a part of the ventricular complex. 2. 2. It represents the part of the cycle in which the supernormal phase occurs. 3. 3. It tends to disappear in some cases of heart disease. 4. 4. Inversion of the U wave or fusion of the U wave with the T wave is found only in patients with damaged hearts. 5. 5. The majority of ventricular extrasystoles fall on the U wave or the part of the cycle where it occurs.