The sympathetic nervous system plays an important role in the genesis of serious ventricular arrhythmias, particularly during myocardial ischemia or after myocardial infarction. In animal models of experimental myocardial infarction, the proposed research will seek: 1) to noninvasively map the distribution of myocardial sympathetic nerves and the distribution of viable perfused myocardium using radionuclide scintigraphy and functional images; 2) to compare the scintigraphic patterns to the regional morphology of sympathetic nerves determined by catecholamine fluorescence microscopy, and to the regional catecholamine content, beta receptor density, and adenylcyclase activity, determined biochemically; 3) to determine the effects of alterations in sympathetic innervation on the electrical stability of the myocardium using programmed stimulation techniques. The results of these experiments may provide important new insights into mechanisms of ventricular arrhythmias in ischemic heart disease, and also may improve identification of patients who are at risk for these lethal ventricular arrhythmias.