A key component of recognizing sudden cardiac death (SCD) risk in the adult congenital heart disease (ACHD) patient is the recognition of heart failure risk for each physiology. The risk of SCD is an accrued phenomenon, representing the influences of anatomy, genetics, surgical and catheter interventions, and long-term sequelae of residual hemodynamic issues. These all lead to a substrate for tachyarrhythmia. It is beneficial in thinking about all of the potential combinations of CHD anatomy and physiologies to categorize SCD risk for the ACHD patient in terms of systemic left-ventricular failure, systemic right-ventricular failure, subpulmonary ventricular failure, the dyssynchronous contractility states due to bundle branch block, and single-site ventricular pacing. This article reviews important issues in arrhythmogenesis for ACHD patients with all of these physiologies and discusses potential cardiac rhythm device-management needs.