The -adrenergic receptors are linked to G proteins The -receptor has three known subtypes Beta-1 receptors primarily regulate myocardial tissue and affect the rate of contraction via impulse conduction Beta-2 receptors regulate smooth muscle tone and influence vascular and bronchiolar relaxation Beta-3 receptors are less well studied but are thought to primarily affect lypolysis and may have effects on cardiac inotropy (Greene Shepherd 2006) In the human heart beta (1)- and beta (2)AR are the most powerful physiologic mechanism to acutely increase cardiac performance Changes in betaAR play an important role in chronic heart failure (CHF) Thus due to increased sympathetic activity in CHF betaAR are chronically (over) stimulated and that results in beta (1) AR desensitization and alterations of down-stream mechanisms (Brodde OE 2006)