Summary This study was undertaken to evaluate the effects of low doses of PBTL on the negative chronotropic responses to coronary artery occlusion (CAO) in the cat. One-minute CAO near the origins of either the left anterior descending or circumflex (CIRC) coronary anteries resulted in a marked bradycardia (−56 ± 5 BPM) and hypotension. Intravenous infusion of only 4 ± 1 mg/kg of PBTL virtually abolished this response. That this negative chronotropic response to CAO was indeed dependent on vagal reflexes was demonstrated by its elimination after atropine (0.5 mg/kg). A PBTL-resistant bradycardia response to CAO was also observed in this study. This bradycardia was found to occur only during CIRC occlusion and was dependent on blockade of blood flow through the sinus node artery. Based on these results it is concluded that study of neural reflexes to CAO in animal models can be markedly impaired by even low doses of barbiturates. In addition, it appears that the cat will serve as an adequate model to investigate development of the sick sinus syndrome, which may be dependent on both neural and ischemic factors.