Hi, Thanks for writing to Health Care Magic, I am Dr Asad Riaz, I have closely read your question and I understand your concerns, I will hereby guide you regarding your health related problem. Angiography or cardiac catheterization is done through one of the major arteries in either your arm or the leg. Arteries are high pressure flow regions. Add to it the fact that they give blood thinner during the procedure which delays clotting of blood at the site where the prick was made. Due to this some blood from that high pressure area escapes from the artery and collects under the skin immediately after tge procedure or during removal of arterial sheath That blood is then broken down by the body to give a purplish color. It is not permanent and will disappear in due time. Meanwhile if it causes pain you may use cold compresses or a sandbad to alleviate it I hope this answered your question, if you have more feel free to ask. Regards Dr.Asad Riaz. General and Family Physician..