The effects of a new calcium antagonist, CD-832, on coronary and systemic hemodynamics were compared with those of nifedipine in conscious dogs. A pair of 10-MHz piezoelectric crystals and an electromagnetic flow probe were placed on the left circumflex coronary artery (LCX) under sterile conditions to measure epicardial coronary artery diameter (CoD) and coronary blood flow (CBF), respectively. CD-832 (30, 100, and 300 micrograms/kg) and nifedipine (3, 10, and 30 micrograms/kg) produced dose-related increases in large epicardial CoD and in CBF. At doses of CD-832 (100 micrograms/kg) and nifedipine (30 micrograms/kg), producing the same increases in CoD and CBF, the duration of increases in CoD and in CBF was markedly longer after CD-832 than after nifedipine. CD-832 and nifedipine produced dose-related decreases in aortic blood pressure (AoP) and reflex increases in heart rate (HR). However, nifedipine produced significantly (p < 0.01) greater tachycardia than CD-832 in equieffective hypotensive doses. These results demonstrate that CD-832 produces sustained dilation of both large epicardial coronary arteries and small resistance vessels and that the degree of tachycardia after CD-832 is significantly less than that after nifedipine.