Our report concerns 18 cases of mitral valve prolapse, all documented by M-mode and D2-mode echocardiographic study. Of these patients three presented severe cardiac arrhythmias and therefore therapeutic treatment was necessary. One of them presented repeated episodes of paroxysmal supraventricular tachycardia and premature supraventricular and ventricular contractions. In another the arrhythmia consisted of numerous ventricular premature contractions. The third presented a sinus tachycardia which necessitated pharmacological treatment. In this study we have examined several forms of arrhythmias associated with mitral valve prolapse and discussed the antiarrhythmic therapy with quinidine, verapamil, amiodarone and propranolol. Since most people with mitral valve prolapse are young, arrhythmia suppression therapy might subject them to a course of treatment for possibly several decades. Therefore, the physician must weigh the risk of antiarrhythmic therapy against the risk of morbidity without therapy in each individual patient.