The endogenous catecholamines, epinephrine and norepinephrine, have profound effects on smooth muscle activity, cardiac function, carbohydrate and fat metabolism, hormone secretion, neurotransmitter release, and central nervous system actions. These activities are mediated by GPCRs belonging to two subfamilies, the α- and β-adrenergic receptors (Bylund et al., 1994). The three members of the β-adrenergic receptor family, β1, β2 and β3, couple to Gs to increase cAMP upon activation. In the heart, the β1 receptor constitutes 70-80% of the β-adrenergic receptors. Activation of cardiac β-adrenergic receptors, acutely increases heart rate, cardiac output, and cardiac automaticity, and chronically increases cardiac myocyte apoptosis. In failing hearts, the β1 subtype is downregulated and desenstitized, probably as a result of increased catecholamine levels. As a result, β-adrenergic receptor antagonists (β blockers) are effective in the treatment of congestive heart failure and arrhythmia (Lohse et al., 2003). Cloned human β1 expressing cell line is made in the Chem-1 host, which supports high levels of recombinant β1 expression on the cell surface and contains high levels of the promiscuous G protein Gα15 to couple the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for agonists, antagonists and modulators at β1.