The objective was to evaluate the influence on cardiac function of a combination of carvedilol, which is a β-blocker and pimobendan, which is a Ca sensitizer. Six beagle dogs (8.7-12.8 kg) were used. The dogs were divided into 4 groups that were placebo, the carvedilol group, pimobendan group, and the combination group. Placebo and carvedilol (1 mg/kg) and/or pimobendan (0.4 mg/kg) were orally administered. Heart rate, arterial blood pressure, left ventricular fractional shortening, and left ventricle internal diameter were measured before and after 3-hour administration. Heart rate was not different in placebo (94 ± 21 bpm), the carvedilol group (88 ± 11 bpm), the pimobendan group (99 ± 22 bpm), and the combination group (100 ± 19 bpm). The pimobendan group (59 ± 3%) and combination group (55 ± 3%) revealed significant elevation of fractional shortening compared with the control (41 ± 5%) and the carvedilol group (40 ± 11%). In the combination group (125 ± 15 mmHg), (P < 0.01) blood pressure fell significantly compared with the placebo (141 ± 14 mmHg), carvedilol group (131 ± 18 mmHg), and pimobendan group (139 ± 22 mmHg). It is suggested that pimobendan indicated a positive inotropic effect in the presence of carvedilol without affecting the heart rate, and the vasodilator action of both medicines was enhanced by the combination of carvedilol and pimobendan.