An elderly man with atrial fibrillation (embolic source), severe central pain with distension, peritonism and marked leukocytosis most likely has acute mesenteric ischemia. The acute abdomen approach names the CT angiogram of the abdomen as the investigation, showing mesenteric arterial occlusion and non-enhancing bowel wall. Ultrasound, small-bowel follow-through and endoscopic ultrasound cannot assess mesenteric arterial flow and would delay diagnosis.