Hi, thank you for asking healthcare magic I understand your concerns Sorry to learn about your brother in law s condition. A heart functioning at 15% is not really a good sign. If nothing is done to improve the condition of the heart, he might not be able to live long and one cannot say with certainty how long he will live. But if something is done, it might prolong his life. Given that he had a valve replacement some years back, it would be important to assess if the heart failure is coming from the valve that was replaced or from somewhere else. Knowing the exact cause of heart failure would be of paramount importance as it would guide the treatment he needs to take. I would advise he sees a cardiologist for proper assessment. I hope I have answered your query I wish him well