My Husband Had Open Heart Surgery Feburary 2016 To Repair

my husband had open heart surgery feburary 2016 to repair aortic anyeursim, and replace mitral valve and maze procedure to help with AFIB. He takes Atenolol (25mg twice daily, lisinopril/hydroclorothiazide (20/12.5 mg twice daily and xarelto (20 mg once daily). He is 61 years old. He is tired all the time and heat bothers him terribly. He has trouble breathing if he is active at all. He is an avid horseman and something as simple as saddling his horse leaves him winded. Much worse in hot weather. Is this the result of the meds? Per cardiologist all seems well with aortic, valve and AFIb.