By the employment of injection methods, it has been possible to demonstrate vascular communications between the coronary arteries and the chambers of the heart. Serial sections and wax-plate reconstructions of these communicating vessels revealed two types which have not been described previously. The first of these communicating vessels are small branches of arteries or arterioles lying near the endocardium. They run a short course and empty directly into the lumen of the heart and, for this reason, they have been referred to as “arterio-luminal” vessels. The second type of vessel arises as a branch of an artery or arteriole and soon breaks up into sinusoids which lie between the muscle bundles and at times between the individual muscle fibers. These vessels have been referred to as “arterio-sinusoidal” vessels, and the sinusoids have been designated as “myocardial sinusoids.”
The histological structure of the “myocardial sinusoids” would indicate that they play a rôle in the nourishment of the heart muscle.