Increasing evidence from clinical trials indicates that carvedilol, an antagonist of alpha1- and beta-adrenergic receptors (ARs), provides an effective treatment for chronic heart failure, whereas nonselective alpha1-AR blockade has an adverse outcome in this disease. It is, however, not clear whether carvedilol exhibits a subtype-dependent impact on three distinct alpha1-adrenergic receptors (alpha1-ARs).We determined binding properties of human ARs for carvedilol using HEK293 human embryonic kidney cells expressing a single AR subtype. Our results showed that the affinities of alpha1D-AR and alpha1B-AR for carvedilol are higher than that of the beta1-AR subtype, a major target in heart failure treatment. The affinity rank order and pKi values of ARs for carvedilol were as follows: alpha1D-AR (8.9)>alpha1B-AR (8.6)>beta1-AR (8.4)>beta2-AR (8.0)>alpha1A-AR (7.9)?alpha2C-AR (5.9)>alpha2B-AR (5.5)>alpha2A-AR (5.3). Furthermore, temporal kinetics of intracellular calcium signaling mediated via alpha1D- and alpha1B-ARs, but not via alpha1A-AR (P<0.01), showed oscillatory patterns with frequencies ranging from 0.3 to 3 per minute in human smooth muscle and HEK293 cells, which were inhibited by the therapeutic concentrations of carvedilol (10 nM) in a subtype-dependent manner. When oscillatory alpha1B-AR and non-oscillatory alpha1A-AR were co-expressed and heteromer receptors were detected with bioluminescence resonance energy transfer and co-immunoprecipitation, carvedilol suppressed only oscillatory component of global cytosolic free calcium change.These results indicate that in addition to beta-ARs, receptor inhibition by carvedilol is directed to alpha1-ARs, preferably to alpha1D- and alpha1B-AR-mediated signaling events, including intracellular calcium oscillations in vascular smooth muscle.