Purpose: The word “herald” means to indicate or sign that something is about to happen. Herald bleeding is defined as an episode of hemorrhage, often accompanied by abdominal pain, which may precede, by hours to weeks, a catastrophic hemorrhage. Case Report: A 57-year old male with past medical history of abdominal aortic aneurysm repair around 15 years ago and peptic ulcer disease diagnosed 10 years ago, presented to the hospital with maroon-colored stool of 2 weeks' duration, along with a few days' onset of melena, coffee ground emesis, and sharp epigastric pain. Medications included Plavix, Protonix, Tramadol, and occasional NSAIDs. Physical examination revealed normal vital signs, and epigastric tenderness without any peritoneal signs. Laboratory analysis showed hemoglobin of 7.1 mg/dL, platelets of 355,000 /μL, and INR of 1.2. A CT scan of abdomen and pelvis with IV contrast showed 1.6 x 1.6 x 1.8 cm saccular aneurysm originating from the termination of the distal abdominal aorta without adjacent acute findings, and 3.1 cm aneurysm infrarenal abdominal aorta with circumferential thrombus. Upper gastrointestinal endoscopy showed L.A. grade B esophagitis and hiatal hernia. Colonoscopy showed a scant amount of blood in colon without any obvious bleeding source. Tagged RBC scan was negative. Second look endoscopy was performed with pediatric colonoscope, revealing 3- 4 mm clean-based ulcer over the fourth portion of duodenum, and two vascular clips were placed. Vascular surgery was consulted and, based on the location of the ulcer on the lateral wall of the abdominal aorta, along with CT finding of induration and inflammation of the aortic graft right at the renal arteries, suspicion was made for aortoenteric fistula (AEF). The patient underwent emergent laparotomy and was found to have AEF. The patient then underwent repair of AEF with a successful outcome. Discussion: AEF is a direct connection between abdominal aorta and gut, most commonly duodenum. It occurs in 0.3-4% of patients who underwent open AAA repair. The most common clinical manifestations are upper or lower gastrointestinal bleeding (herald bleeding; 64%), abdominal pain (32%) and a pulsatile abdominal mass (25%). The proposed theories for the formation of primary ADF are direct wear and inflammatory destruction triggered by infection, foreign bodies or erosions. The characteristic site of formation is the third or fourth part of the duodenum. AEF should be considered in all patients with GI bleeding and a history of AAA or previous aortic revascularization with prosthetic graft. A high index of suspicion is the key. The mortality rate of untreated AEF is 100%. Surgical intervention is mandatory for survival and successful outcome.