Most primary malignancies of the heart, among them also osteosarcoma are found in the left and very uncommonly in the right ventricle. We report a 75-year-old patient with a primary osteosarcoma sited in the right ventricle occluding the pulmonary outflow. The diagnosis was made when the patient was alive, using echocardiography and computerized scan tomography examinations. Like in previous reports on such malignancies, it was far too late for surgical or other therapeutic interventions, and the histological diagnosis was made post mortem.