Summary:The most recent patient in a 13-year experience with 14 patients suffering massive pulmonary thromboembolism requiring pulmonary thromboembolectomy is the focus of this report. This 40-year-old woman not only survived life-threatening acute hypoxemia and right heart failure, but was also found to have developed a unique transudative 700 cc pericardial effusion. Pulmonary artery pressure was 90/30 (mean 50 mmHg), accompanied by 17 mm right ventricular alternans. Systemic alternans and tamponade physiology were absent. This unusual natural model for acute right heart failure illustrates a novel mechanism for pericardial effusion physiology.