The study was performed in 33 patients with echocardiographic diagnosis of mitral valve prolapse (PVM), without any other associated heart disease. A 19 derivations electrocardiogram (ECG) was performed a direct inscription 4 channel Samborns 150 machine at 25 and 50 mm/sec. The purpose of the study was determine the alterations in ventricular depolarization and repolarization, and to correlate them with valve prolapse, as well as with cavitary and parietal dimensions, as measured by M mode and/or two-dimensional echocardiography. Left ventricular hypertrophy detected by ECG agreed with the ECO test in 77%; the sensitivity was of 86% and specificity of 67.5%. Left ventricular hypertrophy detected by ECG was not related with the type of prolapse. Ventricular repolarization alteration was very frequent (84.8%). Association of this parameter with initial notch of R in a VF becomes important for diagnosis suspicion (p less than 0.01). When the abnormal repolarization affected the anterolateral wall, posterior valve prolapse was frequent; when the posteroinferior region was the affected one, the prolapse occurred more frequently in both valves. An important correlation (p less than 0.01) was found between left ventricular dilatation detected by ECO and the abnormal ventricular repolarization.