Four patients with mitral valve prolapse and ventricular tachycardia or fibrillation were described. Case 1 was a 46-year-old man with syncope due to ventricular fibrillation. Case 2 was a 36-year-old woman with palpitation and dizziness due to ventricular tachycardia. Case 3 was a 47-year-old man with palpitation and dizziness due to ventricular tachycardia. Case 4 was a 38-year-old man with syncope due to torsade de pointes. Left ventriculograms showed mitral valve prolapse in all cases. Coronary arteriograms were also normal, supporting a noncoronary etiology of the arrhythmia. Patients with unexplained ventricular arrhythmias should be screened for mitral valve prolapse.