The purpose of this research is to understand the pathogenetic mechanisms underlying the long Q-T syndrome (LQTS), which is strictly related to SIDS, and the SIDS itself. A) LQTS is characterized by ECG abnormalities and by syncopal attacks, due to ventricular fibrillation, which always follows emotional or physical stresses. These attacks depend upon a sudden increase in sympathetic activity and often result in sudden death. A congenitally lower than normal right cardiac sympathetic activity is the most likely pathogenetic mechanism for LQTS. Positive conclusions on the pathogenesis may be reached only by reproducing all the characterisic symptoms in unanesthetized animals during naturally elicited emotional behavior. Cats, with a right stellectomy, will be subjected to emotional situations known to produce violent sympathetic discharges. Electrocardiogram and other variables will be studied while the subject cat is attacked by another cat, used as stimulus, in which a mesencephalic stimulation has elicited attack behavior. B) It seems possible that a natural, transient imbalance in cardiac sympathetic innervation (CSI) might be at the origin of SIDS. There is a strong relationship between SIDS, sleep and apneic episodes. Kittens will be studied, for the possible occurrence of ventricular arrhythmias, during sleep in cages with either a normal or low PO2. Some of them will be studied repeatedly in order to observe possible changes associated with the development of CSI and others will have, at birth, a partial right cardiac sympathectomy. BIBLIOGRAPHIC REFERENCE: P.J. Schwartz: Cardiac sympathetic innervation and the sudden infant death syndrome. A possible pathogenetic link. (Editorial) Am. J. Med. 1976, 60: 167-172.