The coronary angiogram was normal. Myocardial biopsy was performed. The histopathology featured hypertrophic cardiomyocytes with enlarged and hyperchromatic nuclei. There were prominent intracytoplasmic perinuclear vacuoles (E, arrows). There was mild interstitial fibrosis, but no significant inflammatory infiltrate, glycogen accumulation, or amyloid deposition. Electron microscopy showed presence of membrane-bound vacuoles (F). Unlike lysosomal disorders and glycogenoses, the vacuoles appeared empty, reflecting an idiopathic form of vacuolar cardiomyopathy (1). Mitochondria were focally increased, but did not show abnormal cristae patterns or crystalline inclusions. Despite optimal medical therapy, the patient expired soon after discharge.