I am 58 years old male, 165 lbs, have hypertension, but under control with medications (atenolol and amlodipin). I started the popping out under my sternum once in a while since last year in the month of July. It really hurts. It's like someone hits you in the stomach. Later this year, I had atrial fibrillation in the month of February, but I got converted and taking warfarin. Until now I have the popping out under my sternum and I discover when this thing happened I am missing a pulse bit for every pain I feel.

Can you tell me what causing this problem? Sometimes the pain occurs several times in a day, and sometimes a few. It's really scary sometimes.