Mammalian bite wounds are commonly encountered in the emergency department. When patients come early (<8 hours after injury), local infection is not usually evident. At this stage, the issue of providing prophylactic antibiotic therapy arises. We report a complication of a cat bite to the hand in a previously healthy 32-year-old man. This patient did not seek medical treatment immediately after the cat bite, and distinct local infection did not develop. Nevertheless, his course was complicated with acute Staphylococcus aureus endocarditis. We discuss the common pathogens involved in a cat bite infection, including S aureus, and delineate the indications for prophylactic antibiotic therapy after a mammalian bite wound.