In amphibians and reptiles, the heart, being full of blood and having relativly thin walls, is able to get a large enough blood supply from the blood that they are pumping.
In birds and mammals, on the other hand, the heart is larger and has thicker walls, and so needs special arteries to feed into it to provide it with blood.
In the human heart, right after the aorta leaves the left ventricle, two relativly small arteries branch off of it. These are the right and left coronary arteries. A blocking of these arteries by an embolism is a heart attack. Unlike most body tissue, which can survive with an interrupted blood supply, the heart, like the brain, needs a constant blood source if it is to survive. Thus, the coronary arteries are one of the most important blood vessels in the entire body.