CASQ2 and catecholaminergic polymorphic ventricular tachycardia: We aimed to achieve the following objectives: (a) determine the cellular origin of ventricular ectopy, using a tissue-targeted genetic approach that selectively ablates Casq2 gene expression either in the specialized conduction system or in the ventricular working myocardium; (b) determine the anatomic origin of ventricular ectopy in the Casq2–/– mouse CPVT model, using optical voltage mapping of isolated hearts; and (c) model the Purkinje–myocardial junction and determine if and how subthreshold DADs generate ectopic beats.