Heart problems have continued over the years to the point where hills have become a problem here in New Hampshire, Maine, Vermont. So, last year I invested in an electric assist bike (referred to as a pedelec). I bought a trek Ride+ (http://www.trekbikes.com/us/en/bikes/electric_bikes/). It uses the Bionx (http://www.bionx.ca/en/) drive system which only comes into play while pedaling. It provides 4 levels of assistance, and it the 4th level can put you up a hill at 15 mph with no wobbling and with no more effort than pedaling on the flat.
It's a bit heavier (21#) than my other bike, but when I know that I'm dealing with a hilly course, the extra weight is the lesser problem.
It has high-pressure tires (110#), and because the drive motor is mounted in the rear hub, there's no problem mounting the counter on the front hub.
I also use this bike when touring and towing a trailer. Most of the time I just leave the electric shut off, but when I get to a hill it's sure nice to have.
Trek also makes an electric cargo bike if you wanted to haul stuff while you ride.