Ventricular arrhythmias were looked for in 35 patients with mitral valve prolapse. Their frequency is estimated to 35% in the 31 cases studied prospectively. Ventricular tachycardia is observed in 23% of them. Two patients in emergency had to undergo an external electric shock, one of them for ventricular fibrillation. The interest of different methods of detection and investigation of arrhythmia is questioned. Ventricular ectopic depolarizations are usually detected in the first routine ECG when arrhythmia is severe, but the degree of arrhythmia is generally underestimated. The 24 hour electrocardiographic ambulatory monitoring appears as the choice method but it might be inefficient as shown in some observations. In the latter cases, the exercise testing appears as an indispensable complement for the evaluation and long term follow-up of ventricular arrhythmias in mitral valve prolapse.