The sympathetic system is central in the understanding of numerous physiological and physiopathological phenomena. During the last decade, the characterization of a new beta-adrenoceptor subtype, beta(3), in addition to beta(1) and beta(2)-adrenoceptor in the cardiovascular system has changed the view of the roles of the sympathetic system. In heart, beta(3)-adrenoceptor stimulation produce an opposite effect to that induced by beta(1) and beta(2)-adrenoceptors suggesting that in normal heart, the negative inotropic effect induced by the beta(3)-adrenergic stimulation might play a role of a "safety-valve" during intense adrenergic stimulation. In vessels, all beta-adrenoceptors subtypes, beta(1), beta(2) and beta(3), mediate a vasodilation. As beta(3)-adrenoceptors are activated at higher concentrations of catecholamines than beta(1) and beta(2)-adrenoceptors, they could play the roll of a receptor reserve. beta(3)-adrenoceptors are overexpressed in heart failure and hypertension and could constitute a new therapeutic target. In addition, the efficiency of some beta-blockers such as nebivolol could result from an action on beta(3)-adrenoceptors.