Left, Overexpression or lack of sema3A in endocardium causes unbalanced patterning of sympathetic nerves, which alters the potential for lethal arrhythmia. Appropriate sema3A-mediated sympathetic innervation is crucial for maintenance of arrhythmia-free heart. Middle, Up-regulation of secreted nerve growth factor (NGF) from cardiomyocytes in diseased heart may cause lethal arrhythmia and sudden cardiac death (SCD). Right, Down-regulation of NGF in diabetic heart induces denervation of cardiac sensory nerve, which leads to silent ischemia and lethal arrhythmia.