Getting On And Off Feeling Of Fast Heart Rate. EKG Done. Do I Have Any Heart Problem?

Question: I am a 39 year old male that on occasion (it's even happening now as I'm typing this question) my heart will beat really hard for no apparent reason, then goes back to normal. But the way it beats it feels as though it's ready to jump out of my chest, for at least 3 to 4 beats, then return to normal. It;s been going for several years off and on. During this time, I've had everything from EKGs to 24 hour heart monitors to stress tests and all came back negative. It's a scary feeling especially when I lay down at night to get sleep. I'm 6'2 232lbs with minimal exercise experience. I have some stress in my life, along with not the greatest eating habits. No junk food, just poor portion control and awkward eating times.....most of the times just one meal a day. Do I have a heart condition that no one sees?