Reinnervation of the transplanted heart is a con­troversial topic, but there is evidence that both sympathetic and parasympathetic reinnervation can occur, although it is highly variable between patients and even heterogeneous within the same patient [41 nal study, showed that complete reinnervation could take 15 years from the time of transplan­tation. It is uncertain whether exercise improves autonomic control or whether it occurs inde­pendently over time [24, 43]. Reinnervation is significant because resumption of chronotropic control is associated with better exercise capac­ity [44]. Reinnervation also allows for pain sen­sations such as angina [45] and improves the regulation of blood flow to the myocardium [46].

The functional significance of parasympa­thetic reinnervation is unknown. The extent to which it occurs is contentious and not well defined due to difficulties in measuring para­sympathetic activity in the heart. Early studies found that histological evidence of parasym­pathetic reinnervation only appeared 10 years after transplantation [58]. Physiological studies similarly only demonstrated parasympathetic tone after 8 years [59, 60]. These findings may be the result of surgical techniques. The biatrial method was the standard until the mid-to-late 1990s, until the bicaval method predominated. Parasympathetic reinnervation has been demon­strated in patients who underwent bicaval anas­tomosis within a year of transplantation. This could be because the bicaval technique results in both the parasympathetic and sympathetic fibers of the recipient being dissected, whereas in the bilateral technique, approximately half of the sympathetic fibers are cut, and the parasym­pathetic fibers of the recipient are left intact. Surgical dissection of nerves may stimulate axonal regrowth [61].