For testing the efficiency of Bonnecor in intravenous administration (0.3 mg/kg) 36 patients were examined electrophysiologically (31 with paroxysmal supraventricular tachycardias, 5 with ventricular tachycardias). In other 6 patients haemodynamic investigations were performed by means of right-heart catheterization and thermodilution. The supraventricular tachycardias induced by programmed electrostimulation could be interrupted by administration of Bonnecor in 45% of the cases. After the administration of Bonnecor the inducibility of supraventricular tachycardias was suppressed in 11 of the 31 patients. In 2 of the 5 patients with ventricular tachycardia an evocation of ventricular tachycardias was no more possible after an intravenous application of Bonnecor; a medicamentous termination of the ventricular tachycardias had been tried only in one case. Clinically relevant negatively inotropic effects could not be proved. Apart from insignificant malaises in few cases, no side-effects occurred.