We describe the case of an 85-year-old man who presented with a large pericardial effusion. The patient was admitted because of anorexia and general malaise. Chest X-ray revealed an increased cardiothoracic ratio and a small amount of bilateral pleural effusion. Two-dimensional ultrasonographic echocardiography showed pericardial effusions with atrial and right ventricular early diastolic collapse, establishing the diagnosis of cardiac tamponade. Signet-ring cell cancer with pericardial involvement was diagnosed by subxiphoid pericardiostomy. The clear fluid was removed through pericardial drainage. The signet-ring cell carcinoma of the stomach was revealed by gastric fiberscope examination after pericardial biopsy proved malignancy. Virchow lymph node metastasis was also found. We diagnosed the patient with gastric cancer stage IV and suggested him the best supportive therapy. He died of cardiac arrest 1 month after best supportive care.