Arrhythmogenic right ventricular dysplasia is considered to be a slowly progressive disease in which left ventricular dysfunction and congestive heart failure usually appear at the end stage. The initial clinical presentation of this 56-year-old Japanese woman was left-sided heart failure, and the diagnosis was dilated cardiomyopathy, but her left ventricular size and ejection fraction regressed during 10 years of treatment, whereas her right ventricular parameters showed no change.