ABSTRACT – Project 1 Sudden cardiac death due to ventricular arrhythmias and heart failure are the leading causes morbidity and mortality in the United States. The autonomic nervous system plays a major role in the pathophysiology of arrhythmias and heart failure. Neuraxial modulation represents an important avenue for therapeutic intervention. However, the structural and functional determinants of the release of neurotransmitters and peptides in the myocardium in health and disease, which effectively govern cardiac excitability and mechanical function, as well as propensity toward arrhythmias, remain largely unknown. Myocardial scars seen in ischemic and nonischemic cardiomyopathy show abnormal innervation and nerve sprouting at the border zone of scars due to neural remodeling, which have been implicated in the pathophysiology of ventricular arrhythmias. We propose to test “The Spatiotemporal Heterogeneity of Neurotransmitter Release Hypothesis’ – which postulates that scars alter the ultrastructure of nerves and cause non-uniform reflex-mediated neurotransmitter release in the myocardium and represents a crucial/proximate cause of lethal arrhythmias. The major goal of this project is to investigate the structural (myocardial) and functional (neural) changes in the heart that occur because of heart disease and subsequently lead to ventricular arrhythmias. In aims 1 and 2, we will determine the ultrastructure and define the nerve-myocyte stoichiometry and release profiles of neurotransmitters and peptides in normal and diseased hearts in response to physiological stressors and specifically define areas of non-uniform release of neurotransmitters. In aim 3, we will determine the underlying mechanism and potential benefit of vagal nerve stimulation in mitigating the pathological remodeling related to scar formation and autonomic innervation. Regional structural and functional changes in innervation of scar and border zone regions will be studied using high density electrophysiological mapping and real time neurotransmitter and neuropeptide measurements which will be correlated with structural changes at the border zones of infarcts using tissue clearing techniques in a relevant large animal model and in human hearts. Understanding the underlying myocardial and neural mechanisms leading to arrhythmias has the potential to develop and precisely target therapies that inspire therapies for the prevention of sudden cardiac death and progression of heart failure.