Exercising and Heartburn.

You need to follow a GERD-friendly diet, and stick to it. Try keeping a food diary to try and pinpoint any potential trigger foods that you may have developed. I never had the issues you have with burning in your chest when walking, but you might want to talk to your doctor about taking something stronger than Famotidine. Keep in mind that anxiety/stress may cause or make your symptoms seem worse. You did the right thing by seeing a cardiologist to rule out potential heart issues.

Sharon

Prior to my hiatal hernia surgery in April, I had acute reflux symptoms, but exercise never triggered it. I was lifting heavy weights (chest flyes well over 100lbs, deadlifts and squats at over 200lbs, etc) and I would run about 10-12 miles once or twice a week. Walking and running somehow made things better, even though I thought it would make it worse, perhaps because my diaphragm was engaged the whole time.

If I remember what I read correctly, the gut has a nervous system (enteric nervous system) that doesn't "speak the same language" as the rest of your body, and I suspect that there are other parts off the somatic nervous system that misinterpret problems as being related to the digestive system at large, or they can defer pain to locations that seem to be related to, inter alia, heartburn or stomach pains. That isn't to say heartburn isn't a contributing factor, but my experience is that anxiety and stress used to turn some of the problems with my esophagus and stomach into a sympathetic source of pain.

If you can, I would consider trying something like an elliptical at a gym. One where there's not the same impact as walking (you know, like the ones where you swing your legs and kind of glide along). It might help you to see if it's the physical impact that's causing pain, or if the general act of working out is causing some other kind of chest pain.
Just, you know, be careful and listen to your doctors above all.