Most sudden cardiac death (SCD) is associated with coronary artery disease, but little is known about the exact sequence of events that leads up to it and the mechanisms responsible for it. There is a complex interplay between old myocardial infarcts, acute ischemia, the status of the autonomic system, mechanical viability, and electrophysiology that leads to SCD and influences whether tachycardia or bardycardia is the final rhythm. In this project, it is proposed to combine a unique set of technological and physiological resources to study the events surrounding sudden death. An animal model of infarct/ischemia leading to spontaneous SCD has been developing and will be studied in two complementary ways. One set of animals will be instrumented with a custom-developed telemetry system to acquire electrophysiologic and functional data during the conscious, ambulatory state, eliminating the confounding effects of thoracotomy and anesthesia and anesthesia on the incidence and nature of sudden death. Another set of animals will be studied with high resolution, three dimensional mapping to elucidate the mechanisms of the spontaneous arrhythmias that lead to SCD. It is hypothesized that the balance between the vagal and sympathetic arms of the autonomic system and that changes in repolarization properties of the myocardium are predictors of which animals die suddenly and spontaneously and spontaneously as well as the mode of death. It is also hypothesized that spontaneous tachycardia/fibrillation is initially reentrant and that the old infarct is involved in the arrhythmia maintenance. Further, it is hypothesized that bradycardia is associated with pump failure rather than a vagal reflex leading to hypotension. It is proposed to use the data from this research to develop, implement and validate measures that predict imminent SCD on the time scale of seconds to minutes.. Because of the continuous nature of data acquisition over several days when no sustained arrhythmias are observed, it will be possible to determine the specificity as well as the sensitivity of derived predictors. Innovations in telemetry capability, cardiac mapping, and new animal models of spontaneous sudden cardiac death will provide information about the context and mechanisms of sudden death that has not been available before.