Abstract: The presence of a third β-adrenergic receptor (β3-AR) in the cardiovascular system has challenged the classical paradigm of sympathetic regulation by β1- and β2-AR. Although the role of β3-AR in the cardiovascular system remains controversial, increasing evidence suggests that β3-AR serves as a “brake” in sympathetic overstimulation. It is activated at high catecholamine concentrations, producing a negative inotropic effect via nitric oxide production, which is induced by three different nitric oxide synthases. This review summarizes the recent findings regarding the role of β3-AR as an important mediator of NO signaling in the cardiovascular system.