We believe that there was probably some degeneration in cardiac function associated with age in these two animals. The enlarged heart, thickened myocardium, congested lungs, and enlarged liver in the squirrel monkey are diagnostic of congestive heart failure. We believe that a form of cardiac syncope was the cause of death, and that it terminated the syndrome of congestive heart failure before obvious clinical signs developed. Unfortunately, we were unable to perform in vivo cardiac diagnostic procedures on our animals to reach a definitive diagnosis. Cardiac syncope is one of three general types of circulatory failure.
Cardiac syncope is an acute expression of cardiac disease.
In cardiac syncope, there are profound changes in blood pressure and heart rate, such as bradycardia or tachycardia, which result in inadequate blood output from the heart. Syncope may develop along with massive myocardial necrosis, ventricular fibrillation, heart block, and arrythmias 1 . Hypersensitive or hyperactive reflexes, for which the vagus nerve is the efferent limb, may result in reflex inhibition of the heart, manifested as asystole or extreme bradycardia. Sudden death resulting from acute pleural irritation or tracheal irritation of aspirated vomit falls into this group, and there may be no organic heart lesions in these cases 1 . In ventricular fibrillation, paroxysmal tachycardia, and atrial flutter or fibrillation, the heart rate is extremely rapid, and cardiac output is severely reduced or absent 1 .