Rectus sheath hematoma (RSH) is a rare condition caused by hemorrhage into the rectus sheath. It is usually associated with severe cough, abdominal surgery, coagulopathy, and anticoagulation treatment. RSH can be difficult to diagnose and can be misdiagnosed as acute appendicitis, as diverticulitis, or as an ovarian mass. Although RSH usually presents as a benign condition, it can be life threatening, especially in the critically-ill patient. Here, we report a case of fatal RSH due to hypovolemic shock in a critically-ill 73-year-old woman, who had received heparin treatment due to acute myocardial infarction in the intensive care unit and who had been successfully treated by conservative management.