Regurgitation of fat and marrow emboli into coronary veins during resuscitation. Three groups of patients were examined at autopsy for the presence of fat and marrow emboli in the lungs, heart, and other organs. Group 1 was composed of patients with massive pulmonary thromboembolism and attempted cardiopulmonary resuscitation; group 2, patients with pulmonary thromboembolism and without attempted cardiopulmonary resuscitation; and group 3, patients without pulmonary thromboembolism and with attempted cardiopulmonary resuscitation. The results confirm that pulmonary fat and marrow emboli are frequent in those patients who are resuscitated. A novel observation is the finding of multiple coexistent cardiac venous emboli in those resuscitated patients who have pulmonary artery obstruction with pulmonary thromboemboli. These findings suggest that these emboli regurgitate from the right side of the heart to the coronary sinus and cardiac veins in cases of pulmonary artery hypertension. 