I did something similiar, but I dropped to a walk when the HR got up...walked until it recovered, and then jogged a little more, then walked, then jogged, etc. It was very annoying at first because my HR would 'recover' very quickly, but then my it would also skyrocket quickly so my intervals were tiny!

I actually eventually abandoned the process and just followed a couch to 5K walk/run training plan that did it by minutes (instead of HR). I really like martinkap's concept of just running very, very slowly. That makes a ton of sense to me now (after the fact) because for me, walking and running don't use a lot of the same muscles and I often felt like the walking wasn't helping my body at all. Running super-duper slow makes more sense from a physiological point of view.

For running, my cardiovascular fitness has now (after 5 months of this) outpaced my lower body's ability. I ache long before I feel like my heart/lungs need a break!