The chronotropic and inotropic effects of the anti-anginal agent SG-75 (2-nicotinamidoethyl nitrate) and 1-verapamil were investigated in isolated blood-perfused canine atrial preparations. The compounds were administered via the cannulated sinus node artery. 2. SG-75 induced a selective negative inotropic as opposed to a chronotropic effect. Verapamil showed no selective negative chronotropic or inotropic activity. 3. Effects of SG-75 and 1-verapamil on the frequency-force relationship were studied. SG-75 produced a uniform depression of the developed tension at all frequencies tested which the depression with 1-verapamil was greater at higher than at lower frequencies.
