Is there such thing already?
Collect all 12 leads signal via bluetooth connection to a Iphone/Mobile device.
Whenever I do a 30,60 minutes exercise in the GYM, the system will collect all the data and store them in my personal cloud.
Whenever I did annual checkout with my PCP, I will go over the data/chart with him/her and see if there are any abnormalities that might trigger any concerns.
If they spot any potential issue, than we have more info to do proper stress tests in the hospital and lab setting.
Would this kind of device/process be valuable from your ( Doctor's ) point of view?
BTW, I have background in embedded system, cloud backend, and some mobile app, if any doctors think these kind of monitoring devices are useful. I can definitively love partner up working on such project. My mom suffered from heart attack a few years back - so this topic trigger a personal nerve for me.
For data collection or your own interest, a proper 12 lead ECG is a great reference item; but again if the machine is like [1] you are only going to get this simple trace that doesn't tell you much; even serial ECG's on a normal healthy patient (or even someone with moderate heart disease) will be almost perfectly normal day to day, month to month at rest.
So I would be inclined to suggest that it is a bit of a waste of money from any attempt at home diagnostics, however if you were concerned about your cardiovascular risk you should discuss it with your doctor.
[1] http://www.amazon.com/Medical-Real-Handheld-Portable-Monitor...