TNNI3K and Supraventricular tachycardia: Up to now, 7 TNNI3K (troponin-I interacting kinase) variants have been reported,1–7 from which 3 with moderate-to-strong genetic evidence, for example, multigenerational cosegregation.1,2,4 Patients harboring variants in TNNI3K present with several cardiac phenotypes including dilated cardiomyopathy (DCM), cardiac conduction disease (CCD), and supraventricular tachycardias (SVT).