Ventricular arrhythmias are common in patients with mitral valve prolapse. Ten patients with echocardiographically confirmed mitral valve prolapse and documented ventricular arrhythmias were included in this study. The aim was to assess the value of combined alpha- and beta-blockade (labetalol) compared with beta-blockade alone (propranolol) in the management of ventricular arrhythmias in these patients. The study was performed using physiological stress, such as the Valsalva manoeuvre, isometric exercise and treadmill exercise, to initiate ventricular arrhythmias before and after intravenous propranolol or labetalol and to document arrhythmias during 24 hour electrocardiography before and after oral medication. Labetalol and propranolol decreased the heart rate and blood pressure response to these manoeuvres to a similar extent but labetalol was more effective in the control of the ventricular arrhythmias. These findings suggest that alpha adrenergic receptors may play a role in the pathogenesis of the ventricular arrhythmias in mitral valve prolapse syndrome and that labetalol offers an alternative treatment for the management of this condition.