Thinking you are having a
heart attack or
heart failure is one of the most common symptoms of panic
attacks. Of course thinking it does not make it reality. Your thoughts and worries are real, but your self diagnosis is not. When you feel an attack coming on, talk yourself through it. Remind yourself that you've been here before and it has always been nothing. Breath calmly, and try not to hyperventilate, that will only make your symptoms worse.
Do you see a therapist?