We developed methods for identifying βadrenergic receptors in human right ventricular endomyocardial biopsy tissue with the radioligand (−)[1251]iodocyanopindolol (ICYP). Specific ICYP binding in a crude, high-yield membrane preparation derived from endomyocardial biopsy tissue was high (specificity > 90%), of high affinity (KD around 20 pM), saturable and stereospecific for the (−) vs the (+) isomer of isoproterenol. Subjects with mild-moderate and severe biventricular dysfunction had respective decreases in β-adrenergic receptor density of 38.2% and 57.7% when normalization methods were averaged, with no significant differences in ICYP dissociation constant. A subgroup of subjects was subdivided by left ventricular ejection fraction (LVEF) into those with mild cardiac dysfunction (LVEF < 0.50 > 0.40) and severe heart failure (LVEF < 0.20) and given graded sequential infusions of dobutamine and calcium gluconate. Those with severe cardiac dysfunction had marked impairment of the dobutamine dP/dt and stroke work index response, whereas these responses to calcium did not differ in the two groups. These data indicate that in the intact human heart (1) endomyocardial biopsy may be used for direct analysis of β-adrenergic receptors. (2) heart failureassociated myocardial f3-adrenergic down-regulation begins with mild-moderate ventricular dysfunction, (3) reduction in myocardial βreceptor density is related to degree of heart failure, and (4) βreceptor down-regulation is associated with pharmacologically specific impairment of the β-agonist-mediated contractile response.