In the past decade there has been an increasing awareness of distinct, potentially lethal heritable cardiomyopathic and channelopathic syndromes as they pertain to sudden cardiac death in infants and children. This review highlights current clinical and molecular findings of two highly relevant structural cardiac abnormalities evident at autopsy, namely hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, as well as the cardiac channelopathies of long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, and short QT syndrome, which may account for one third of autopsy-negative sudden unexplained deaths (SUDs) during childhood and adolescence. We also explore the role of postmortem genetic analysis (molecular autopsy) in cases of SUD, provide a critical analysis of the current spectrum and prevalence of channelopathies as the pathogenic basis for sudden infant death syndrome (SIDS), and provide a brief synopsis on genetic testing for such potentially lethal cardiac disorders.