Autoradiographic techniques have been employed to demonstrate the distribution of the postganglionic sympathetic cardiac fibers originating from the right stellate ganglion in 3 cats. After exposing the ganglion through a right thoracotomy, a total of 500 muCi of tritiated leucine was injected into the right stellate ganglion of each cat. After 3 days the animals were sacrificed by vascular perfusion. The injected ganglia, the heart and great vessels were processed for autoradiography. The majority of the right stellate ganglionic fibers travelled between the trachea and aortic arch, and entered the cardiac fibers travelled between the trachea and aortic arch, and entered the cardiac plexus. Continuing through the plexus, these fibers coursed between the ascending aorta and the pulmonary arterial trunk to form a periarterial plexus around the left coronary artery and its branches. Most of the fibers followed the distribution of the ventral descending branch of the left coronary artery; a few followed the circumflex artery. A conspicuous subepicardial plexus was derived from the periarterial plexus and was most prominent in the cranial half of the left ventricle. Other fibers arising from the right stellate ganglion descended between the cranial vena cava and the right branch of the pulmonary artery. These ramified on the dorsolateral surface of the right atrium, and also formed a large bundle which passed caudally through the interatrial septum.