Normally blood flows from the heart to the arteries of the body. The arteries branch and get smaller until they become a capillary, which is just a single cell thick. In this way blood pressure drops to very low levels that the thinner walled veins can cope with. In an Ateriovenous Malformation (AVM), usually early in life, arteries connect directly to veins. This is a high-pressure shunt or fistula. Veins are not able to handle the pressure of the blood coming directly from the arteries. The veins stretch and enlarge and create what we call a “nidus”. Usually there are multiple feeding vessels in an AVM and many draining veins.