The clinical and laboratory findings of 28 patients identified as having late pericardial effusions were examined. Eleven of these patients were asymptomatic; 9 patients had moderate symptoms including fatigue, malaise, weight gain, and dyspnea on exertion, and 8 patients with similar symptoms had evidence of cardiac tamponade. Ten patients underwent right heart catheterization in the intensive care unit; normal hemodynamics were confirmed in 4 and cardiac tamponade in 6 patients. Pericardiocentesis was effective in decompressing cardiac tamponade in 7 of 8 patients. One patient required operative subxiphoid drainage after unsuccessful pericardiocentesis. In addition, 5 patients with moderate clinical symptoms and pericardial effusions, who did not have cardiac tamponade, underwent pericardiocentesis because of a need for chronic anticoagulant therapy. The remaining patients were managed successfully by observation, discontinuation of warfarin when possible, fluid restriction, and diuretic therapy. All but 1 patient was symptomatically improved. A diagnostic and therapeutic schema is presented as an aid to early recognition of this troublesome and potentially lethal complication.