Abstract
Phenoxybenzamine increased the force of contraction and rate of the heart and lowered the blood pressure of dogs in pentobarbitone anaesthesia. This was preceded by depression of cardiac contractile force and a rise in blood pressure when phenoxybenzamine was injected following ganglion-blocking drugs or atropine. The positive inotropic and chronotropic and the hypertensive effects of phenoxybenzamine were prevented by pretreatment with reserpine or guanethidine.