The central nervous system (CNS) may play a larger role than previously thought in the development of ventricular fibrillation after coronary artery occlusion. The probability of ventricular fibrillation after complete, permanent occlusion of the left anterior descending coronary artery was 52% in conscious control pigs. After the administration into the lateral cerebral ventricle of tyrosine, the amino acid precursor of the catecholamine neurotransmitters, 100% of the animals developed ventricular fibrillation. After tyrosine plus propranolol, a beta-adrenoceptor antagonist, only 9% of pigs developed ventricular fibrillation. Treatment with propranolol alone did not affect the outcome. Catecholamine synthesis in the CNS may be associated with the development of ventricular fibrillation after coronary artery occlusion.