Parkes Weber syndrome is characterized by vascular abnormalities known as capillary malformations and arteriovenous fistulas (AVFs), which are present from birth. The capillary malformations increase blood flow near the surface of the skin. They usually look like large, flat, pink stains on the skin, and because of their color are sometimes called "port-wine stains." In people with Parkes Weber syndrome, capillary malformations occur together with multiple micro-AVFs, which are tiny abnormal connections between arteries and veins that affect blood circulation. These AVFs can be associated with life-threatening complications including abnormal bleeding and heart failure.