It sounds like premature heart beats commonly known as PAC's or PVC's depending on if they originate in the upper or lower chamber of the heart. If your ECG, stress test anad echo were normal, they are definately no big deal. Also if you didn't have any during one of your tests, they wouldn't show up. You would probably have to wear a holter or monitor to capture them. They are completely benign with your normal workup but that can be really hard to believe at first. I've had them for a long time and I still hate them! If I only have a few, I can ignore them but sometimes there can be quite a few for many hours. Then I have a hard time with them.