Changes in number and/or affinity of cardiac neurotransmitter receptors have been associated with myocardial ischemia and infarction, congestive heart failure, cardiomyopathy, as well as diabetes or thyroid-induced heart muscle disease. These alterations of cardiac receptors have been demonstrated in vitro on membrane homogenates from samples collected mainly during surgery or post mortem. The disadvantage of these in vitro binding techniques is that receptors lose their natural environment and their relationships with the other components of the tissue. In vitro autoradiographic techniques in human tissue offer several advantages over homogenate-binding techniques: an increase in sensitivity and the possibility of anatomic resolution allowing light microscopic mapping of relationships between the distribution of specific cell populations and neurotransmitter receptors. However, the evolution of receptor changes as the disease progresses or as the effect of a drug cannot be analyzed. With the advent of positron emission tomography it is now possible to achieve, non-invasively, quantitative determination of regional biochemical processes in the heart.