Could I Have A Serious Heart Problem ?

I m a 21 year old male, a little bit overweight (Maybe a stone or so) but relatively fit. Just recently, I ve been getting an electric pain in the left side of my chest which lasts anything from a few seconds to a couple of minutes. I went to an NHS walk-in centre today to get checked out and the nurse performed an ECG . She looked at the results and said they were fine. Then, a few hours later she rang me back to say that there s nothing to worry about , but a doctor s looked at the results and is a little concerned. The way she put it was my heart beat was very slow (Getting slower when I breathed in) and had some irregular blips . I need to see a GP immediately and if I get any more pain to go straight to A E or call ambulance if it s severe. Of course my GP will be able to tell me more, but are these symptoms characteristic of any well known condition, or is it unlikely that I have anything to worry about. I just want to put my mind at rest tonight. Thanks.