A 78-year-old man admitted to our hospital with signs and symptoms of right ventricular failure, consisting of severe edema of the scrotum and the penis, ankle edema, hepatomegaly, and a history of asthenia associated with a recent weight loss. Two-dimensional echocardiography showed an intracavitary mass in the right atrium and a moderate pericardial effusion; the remaining structures were normal. To better define the origin of this mass, transesophageal echocardiography was performed. The mass extended from the inferior vena cava with no sites of attachment to the atrial wall. The mass was elongated, mobile, with a triangular termination near the tricuspid valve, without signs of right ventricular obstruction. An abdominal-pelvic CT scan demonstrated the origin of the mass at the superior pole of the left kidney extending through the renal vein and the inferior vena cava into the right atrium. The mass was surgically removed and the pathological examination revealed a renal cell carcinoma (hypernephroma) of the clear cells subtype. After surgery, the patient did well with the resolution of the picture of right ventricular failure.