Cardiac hamartomas are very rare and are demarcated masses of enlarged, hypertrophied, mature myocytes and collagen tissue. Cardiac hamartomas are generally circumscribed in the right ventricle or atrium, but not reported in the crista terminalis (CRT). The CRT is crucial in electrophysiology, is related to arrhythmogenesis, and is targeted by radiofrequency catheter procedures. Previous works only described the benign natures of prominent CRT using non-invasive methods. This study describes an unusual cardiac hamartoma originating from the CRT and extending toward the tricuspid valve. Microscopically, this hamartoma comprised dense collagen and adipose tissue, mixed with hypertrophy, but with disarrayed cardiomyocytes. An irregular gap junction, connexin43, was demonstrated in this cardiac hamartoma.