We presented an unusual arrhythmogenic right ventricular cardiomyopathy (ARVC) case of a late-60s elderly man's death, due to severe pericardial/pleural effusion and ascites, and arrhythmic events, with unique pathological features. The hypertrophic heart grossly displayed yellowish to yellow-whitish predominantly in the variably thinned wall of the dilated right ventricle. Microscopic findings showed diffuse fatty/fibrofatty replacement in not only the right but left ventricular myocardium, together with an outer lymphoplasmacytic infiltrate. According to the lipid contents analysis, the triglyceride content, but not the cholesterol content, in our patient's right and left ventricular cardiac muscle was much higher than that in the control subject. We propose that this unique triglyceride deposition in our possibly late-onset ARVC case might be one of new clues to understand its enigmatic cause. Further prospective studies are needed to validate the presence and significance of a greater volume of triglyceride deposit, after collecting and investigating a larger number of early and late-onset ARVC cases examined.