mitral valve prolapse
"I was born with mitral valve prolapse and started having palpitations when going through a lot of stress in my mid-30s.  I was started on Atenolol 25 mg per day.... then noticed about 10 years later that my heart rate was going up again and had bouts of palpitations.  My Dr just adjusted the dosage to 50 mg per day.  I have asthma also but Theophylline ER 200 mg taken twice daily takes care of the asthma."