Arteriovenous malformations (AVMs) are defects in your vascular system. The vascular system includes arteries, veins, and capillaries. Arteries carry blood away from the heart to other organs; veins carry blood back to the heart. Capillaries connect the arteries and veins. An AVM is a snarled tangle of arteries and veins. They are connected to each other, with no capillaries. That interferes with the blood circulation in an organ.