The role of nervous and ionic factors in the genesis of the sudden death associated with acute myocardial infarction will be investigated using a combined approach involving three projects. The first project "Potassium Loss During Myocardial Ischemia" is concerned with changes in extracellular potassium ion activity as a consequence of changes in pH or oxygenation. The second project "Electron Microprobe and Ultrastructural Analysis of Ischemic Myocardium" is directed towards determining the distribution of ionic changes in normal and ischemic myocardium. The effects of cardiac innervation will also be examined. The third project "Left Stellectomy in the Prevention of Sudden Death" investigates the role of the cardiac innervation upon the occurrence of fatal arrhythmias during acute coronary occlusion. The specialized methods to be used in this program involve ion-selective microelectrodes for measuring ionic activities in extra- and intracellular fluids, transmembrane flux measurements with isotopes, intracellular concentrations with atomic absorption spectrophotometry, and electron microprobe analysis of tissue electrolytes, ultrastructural examination of the same tissues, and instrumentation of chronic animals. In addition, techniques of nerve stimulation, electroneurography, Doppler flow and strain gage blood pressure will be used. BIBLIOGRAPHIC REFERENCES: Kunze, D.L., W.R. Saum and A.M. Brown. 1977. Sodium sensitivity of baroreceptors mediates reflex changes of blood pressure and urine flow. Nature. (In press). Schwartz, P.J., R.L. Verrier, and B. Lown. 1977. Effect of stellectomy and vagotomy on ventricular refractoriness in dogs. Circ. Res. (In press).