2 litres of blood is rather a lot. I would go find a Doctor and take them to your wife immediately. I have no idea why 2 litres of blood would have been lost, but it must be something serious.
My wife had a heart attack and is in ICU right now got her up in a chair of the nurses did she had a bowel movement and lost 2 L of blood and have been waiting for six hours for a doctor to come in and look at her what do I do they did give her more blood but still no doctor
Bright red blood is usually from a hemorrhoid. Bleeding further up the digestive track typically turns the stool very dark. Do check with your doctor. They can easily check for hemorrhoids and may give you an occult blood test to do at home. If you're having bleeding every day, they may want to do a sigmoidoscope and check out your colon. If you're straining while trying to pass a stool, it would be a good idea to increase your water and fiber intake. Years of straining won't do your colon any good. Take care.
Check with your doctor. I am not a doctor, but I know that it can be a result of a benign condition, or can be from something more serious. You probably want to post this question in another forum...this is not a heart related question.