A 76-year-old-woman, who had undergone endoscopic resection of a gastric polyp 2 years previously, had a cardiac tumor incidentaly pointed out on an abdominal ultrasonographic image. Echocardiography showed a solid round mass (34×25 mm in diameter), attached by a short stalk and which was floating on the right ventricular outflow tract and prolapsing over the pulmonary valve during systole. We suspected right ventricular myxoma. Urgent surgery was performed under cardiopulmonary bypass. After aortic clamping, the trunk of the pulmonary artery was opened near the right ventricule. The tumor was found under the pulmonary valve, attached to the anterior papillary muscle and chordae of the tricuspid valve. The tumor was completely excised with a piece of the papillary muscle and chordae. After right atriotomy, mild tricuspid regurgitation was seen on a water test. After we performed tricuspid annuloplasty and chordplasty with artificial chordae, a second water test did not show any tricuspid regurgitation. The postoperative course was uneventful, and she was discharged on the 13th postoperative day.