If you have complications, you may pass blood in your faeces because of weakening of the blood vessels in the diverticula. Blood from the lower part of the large intestine shows as blood in your faeces. Blood from higher up, eg your stomach, tends to make your faeces black and tarry. Scar tissue can form around one of the inflamed diverticula causing narrowing of the bowel or blockage. If diverticula burst, they can cause the lining of your abdomen(peritoneum) to be inflamed and swollen. This is called peritonitis. If you have peritonitis, you may need emergency surgery.
Attribution: BUPA