Tiring can be caused by severe aortic stenosis but you don t say how long he has been like this for? Is this a new thing or has he always been like this and his Doctors are already aware of the situation? It needs to be determined if his tiredness and lack of energy is due to his heart problem or not, if it is and this is a new thing then it could be an indication that the stenosis has got worse, in which case he needs a sooner hospital appointment. Even mild stenosis can worsen over time. It s important you consult your GP this week. I don t know how much your Doctors have explained to you but basically, because the valve is narrowed, the heart has difficulty pumping blood to the body. If the stenosis is severe then he will of course be symptomatic. Typical symptoms are unusual tiring, chest pain, dizziness or fainting. Often if the stenosis is severe then surgery is required to enlarge the valve opening etc. Please make an appointment to see your GP this week. Before you attend the appointment, write down all the questions you want to ask. If you don t understand something then you must ask your GP to explain it to you. Do not leave the surgery until you fully understand the situation.