A right atrial mass was discovered with transthoracic cardiac ultrasound in a complaint-free, 81-year-old man at his yearly cardiological checkup. Further investigation of the mass with transesophageal cardiac ultrasound showed a well-defined nodular mass of approximately 3 × 3 cm, in close proximity to the posterior wall of the right atrium. The patient underwent an F-FDG PET/CT, which showed a right atrial mass with very high FDG uptake, suggesting a malignant process. The mass was surgically removed, and anatomopathological assessment revealed an intimal sarcoma, which is a very malignant tumor and an extremely rare occurrence at this location.