Morning, compumac, I was diagnosed as needing a triple bypass and was told I had to do some 2 miles a day. That was last December and out walking was very cold, so I bought a treadmill from Tesco's which was less that £155 and have used virtually every day since. it has speeds of 1 to 10 kph and is horizontal at all times. Speed is set manually and can be changed whilst walking.
Best of luck, whatever you decide.