My Husband Easily Gets Tired Walking Even Short Distances And

My husband easily gets tired walking even short distances and having shortness of breathe. All his echocardiogram; ct scan, ex ray and blood works came back normal. His doctor said, nothing much they can do with him. Please let us know what else do we need to do. He used to walked 10 miles a day at work and have no issues but now he cannot do his regular activities. If this is free consultation please get back to me if not never mind.