Glad to hear that you're doing well. I'm a physical therapist who has worked with many patients who have undergone aortic valve replacement surgery. What you have heard is correct. People often feel sluggish and tired (and sometimes depressed) after cardiac surgery. It's common and it does get better as each month goes by. The best advice I could give you is to listen to your body. When you feel like you need a break, take one. Rest breaks are ok. Trying to do a little more each day is fine, but within reason. Don't overdo it, you'll get there in time. Good luck.