We report a case of a 70-year-old woman admitted with symptoms of decompensated heart failure. Magnetic resonance imaging revealed lipomatous hypertrophy of the interatrial septum with partial upper right atrial inflow obstruction, partial obstruction of the right ventricular outflow tract, and excessive accumulation of adipose tissue in the pericardial space. The patient underwent excision of the septal lipomatous mass, which relieved the right ventricular outflow obstruction.