My father in law is feeling ill.  he is in his early 70s with heart problems.  He says he just doesnt feel weel, didnt sleep last night but was VERY tired, legs are so weak he cant walk, and this morning had a black stool.  Could he be having congestive heart failure?
Hello Black stools indicates blood loss in stools which means he may be having low hemoglobin. Low hemoglobin leads to all his symptoms and also aggravates heart failure. So its important that he undergo stool blood testing, hemoglobin and consult a cardiologist if he is receiving aspirin or clopidogrel medicine in order to temporarily withhold it. Also, he needs to undergo ultrasound of the abdomen for ruling out other causes. Hope this helps you and get back if you have any doubts.