Some are in fact hereditary, some are just the luck of the draw. I have hereditary AVMs in my lungs, liver and GI tract. My cousin has Brain & Lung AVMs. We have HHT, which is hereditary. We have numerous Telangiectasias: nasal, GI, skin, mouth, vagina - which are malformed vessels. They bleed constantly. I now take a medication used for tumors, to shrink the vessels that feed the telangiectasia/AVMs to slow the bleeding & potential for bleeding.