Misplaced caval filter and subsequent pericardial tamponade. Use of the Greenfield filter for partial caval interruption is generally accepted as the most reliable mechanical method of pulmonary embolus prophylaxis. However, there have been reports of a variety of (usually nonfatal) complications. We report here the near-fatal complication of acute pericardial tamponade after misplacement of a Greenfield filter. Because of the filter's unusual location, retrieval required cardiopulmonary bypass, profound hyperthermia, and circulatory arrest. 