Effects of CD-832 on isoproterenol (ISO)-induced myocardial ischemia were studied in dogs with partial coronary stenosis of the left circumflex coronary artery and findings were compared with those for nifedipine or diltiazem. In the presence of coronary artery stenosis, 3-min periods of intracoronary ISO infusion (10 ng/kg/min) increased heart rate and maximal rate of left ventricular pressure rise, which resulted in a decrease in percentage segmental shortening and ST-segment elevation of the epicardial electrocardiogram. After the control ISO infusion with stenosis was performed, equihypotensive doses of CD-832 (3 and 10 micrograms/kg/min, n = 7), nifedipine (1 and 3 micrograms/kg/min, n = 9) or diltiazem (10 and 30 micrograms/kg/min, n = 7) were infused 5 min before and during the second and third ISO infusion. Both CD-832 and diltiazem, but not nifedipine, significantly reduced the increase in heart rate induced by ISO infusion. In contrast to nifedipine, CD-832 (10 micrograms/kg/min) prevented the decrease in percentage segmental shortening from 32 +/- 12% to 115 +/- 26% of the control value (P < .01) and ST-segment elevation from 5.6 +/- 1.0 mV to 1.6 +/- 1.3 mV (P < .01) at 3 min after ISO infusion with stenosis. Diltiazem (30 micrograms/kg/min) also prevented the decrease in percentage segmental shortening from 34 +/- 14% to 63 +/- 18% of the control value (P < .05) and ST-segment elevation from 4.7 +/- 0.7 mV to 2.1 +/- 0.7 mV (P < .01) at 3 min after ISO infusion with stenosis. These data show that CD-832 improves myocardial ischemia during ISO infusion with stenosis and suggest that the negative chronotropic property of CD-832 plays a major role in the beneficial effects of CD-832.