Without knowing what the specifics to your case, I can not turn around and guess what the final outcome will be, but hopfully your first Dr is right. You will pass the medical. I too, have been caught in a cardiac loop of testing. I have a fairly intimate knowlege of both my cardiologists waiting room. The thing is, for any deviation outside the published norm, there is a seeminly unending battery of tests.
Everyone has abnormal beats from time to time, and they have stipulated guidelines on what is acceptible for aviation standards. At the ripe age of 36 I had a series of cardiac events. (I was not having a good chrissy or new year) Subsequently I am grounded and have been since last christmas due to the delays in getting from specialist to specialist. Since then the piles of reports have been getting taller, and they have put the whole episode down to a virus or something similar. Believe me, I was pretty edgy after the after the third one! and pretty reluctant to come anywhere near pprune... It was too depressing.
Since then, I have had 12 lead ECG, Echocardiographs, 24 hour monitoring, stress ECG and all they have been finding is variations of normal. What they were looking for was a condition call R on T, which can develop into a life threatening arrhythmia in younger people. They didnt find it, and I now know what my heart looks like,what conditions the valves are in and so on. The Echo was the coolest medical test I've done, especially as the ultrasonographer explained what she was doing on the way through.
So given you have a normal healthy life, and no symptoms to speak of, I suggest they are just ticking off the relevant boxes. The cardiologist will have the final recommendation. So, just sail along with it, dont panic (that give false resting heart rates!) and let them tick the boxes until you hold the medical.
There are worse tests than an ambulatory 24 hour Holter monitor, believe me. And good luck, it sounds as if you are in good hands.