1. Tabernanthine produced, in anaesthetized Rat and Dog, bradycardia and hypotension which remained after atropine or vagotomy. Bradycardia was significant from 0,5-0,8 mg . kg-1. The degree of hypotension depended upon the anaesthetic. 2. Effects of tabernanthine on cardiovascular parameters in anaesthetized Dog (blood pressure, heart rate, cardiac output, left ventricular pressure, dp/dt, cardiac potency, cardiac work and ventricular ejection volume) are described. There were no changes of noradrenaline, acetylcholine, tyramine or 5-hydroxytryptamine-induced cardiovascular effects by tabernanthine. 3. Bradycardia occurred also after per os tabernanthine administration in unanaesthetized Dog. 4. Tabernanthine reduced Rat isolated and perfused heart frequency. 5. It is suggested that tabernanthine has a direct action on myocardial muscle, probably by modification of calcium exchanges.