Suggest Treatment For Large Bruise On Abdomen

My husband has developed a large (about 4 in x 2 in) bruise on his abdomen (lower right). He is experiencing no pain, and has no recollection of injuring the area. He is 64, 5'11", 200 lb. Aside from surgery 2 yrs ago to replace a deformed aortic valve, and controlled high blood pressure, he is in excellent health.