Hepatoma has a tendency to spread into the venous system, but intracavitary cardiac extension or metastasis of hepatocellular carcinoma is an uncommon form of cardiac malignancy. When the carcinoma grows from the hepatic vein into the right atrium, the right atrial tumor thrombis may hinder the blood flow. Therefore, these patients have the risk of sudden death. In the past, antemortem diagnosis of right atrial tumor thrombi in patients with primary hepatocellular carcinoma was difficult. But, echocardiography allowed easy detection of the intracardiac tumor thrombi. We describe two cases of hepatocellular carcinoma with right atrial tumor thrombi. In these cases, the right atrial tumor thrombi was detected by two-dimensional echocardiography. Recently, successful surgical removal of the right atrial tumor thrombi are reported in several cases. We advocate performing echocardiographic examination in patients with hepatoma who have cardiac symptoms and signs.