I have had a fairly debilitating level of OI for years. As I posted on another thread, I recently had a pacemaker implanted due to sick sinus syndrome. The amazing and unexpected side effect is that it has very noticeably improved my OI. I did a poor man's tilt table test a few weeks after the surgery and my numbers were way, way better and I could stand much longer. My base rate was set at 60 in the hospital. Today, 5 weeks later, I had a followup appointment, told my electrophysiologist how much my OI had improved and asked if she could bump up the base rate to 70. She did and there is even more improvement though I'll be checking out what I can do in the next weeks. I live next door to a health food store and have a cart to bring my shopping home (including 3 gallon bottles of water). I had been unable to pull the cart for several years--I had to stop and rest every 25 ft. Today I loaded it with a 3 gallon bottle of water and the rest of my grocery shop, and pulled it home with no problems! I am thrilled and just wanted to share with others that a low heart rate may effect OI for some. I am very thankful and am hoping that this will allow me to exercise a bit more.