A 72-year-old female presents to the emergency department reporting an episode of a large volume of bright red blood per rectum four hours earlier. She states that the toilet was filled with blood. The patient reports that the bleed was painless and was not associated with a bowel movement, and she thinks it stopped about two hours ago. She has never had rectal bleeding before. She denies fevers and chills. A colonoscopy two years ago only demonstrated a few diverticula but no polyps. She has not lost weight recently. Her past medical history is significant for hypertension and chronic constipation. She has had no prior surgery. On physical examination, her blood pressure is 135/88 mmHg, and her heart rate is 80/min. She is afebrile and has a normal respiratory rate. She appears to be pale and anxious. Cardiac and lung examinations are normal. Abdominal examination reveals no surgical scars and no masses. Her abdomen is nondistended, has normal bowel sounds, and is nontender to palpation, without rebound tenderness or guarding. Digital rectal examination reveals gross blood in the rectal vault but no masses. Anorectal examination shows no fissures, and anoscopy shows no internal hemorrhoids. Laboratory values reveal hemoglobin of 8 g/dL (normal 12–15.2 g/dL), hematocrit of 24% (37–46%), and normal mean corpuscular volume (MCV).