Stimulation of beta1- and beta2-adrenergic receptors (ARs) in the heart results in positive inotropy. In contrast, it has been reported that the beta3-AR is also expressed in the heart and that its stimulation leads to negative inotropic effects. The aim of this study was to investigate the expression of beta3-AR in age-related heart-failure rats and its relevance to left ventricular dysfunction. Aging male Wistar rats were divided into young and aging groups according to age, and each group included sham-operation and heart-failure subgroups. Left ventricular end-diastolic pressure (LVEDP) and the ratio of left ventricular weight to body weight (LV/BW) were significantly higher for the aging heart-failure versus young heart-failure and the heart-failure versus sham-operation groups (P < 0.01, respectively). However, the left ventricular end-systolic pressure (LVESP) and the maximal rate of rise or fall of left ventricular pressure were all significantly lower for the aging heart-failure versus young heart-failure and the heart-failure versus sham-operation groups (P < 0.01, respectively). beta3-AR protein levels increased significantly when heart failure worsened in aging rats. These results suggest that beta3-AR expression in age-related heart-failure rats and left ventricular function were highly correlated.