Sprouting axons follow the developed coronary veins. Dorsal views of whole-mount hearts stained for neuronal marker Tuj1 (green) and pan-endothelial marker PECAM1 (red). At E15.5 in mice, Tuj1-positive sprouting axons (green, closed arrow heads) are found in relative close proximity to the larger coronary veins (Red, open arrow heads). RCV = right cardiac vein, mLCV = medial branch of the left cardiac vein, lLCV = lateral branch of left cardiac vein, LV = left ventricle, RV = right ventricle. Adjusted from [151], with permission from Nam, et al., Development; published by The Company of Biologists Ltd., 2013.