Quinazosin is a diaminoquinazoline derivative patented by Pfizer, Chas., and Co., Inc. as a hypotensive agent. Quinazosin acts as adrenoreceptor antagonist and in preclinical studies lowered systolic blood pressure in conscious hypertensive dogs, without having any significant effect on their heart rate. Quinazosin lowered blood pressure and reduced total peripheral vascular resistance, while the duration of these effects was dose-dependent. In cats, Quinazosin reduced or reversed the pressor effects of epinephrine, but did not alter those of angiotensin amide.