I would say if your O2 sats were bad your heart may have been pumping harder to compensate and if the O2 stats got better then subsequently the heart could slow down and rest and not need to beat as fast and so the pulse would indeed be slower. What kind of change in O2 Sat and beat are we talking about. Too fast to too slow or is it that you sense the heart is exceptionally slow now? Were the O2 sats in or out of range? What are your symptoms and why do you suspect O2 sats are the issue?
The normal oxygen saturation is 95-100 %. The better oxygenated you are the less your heart has to work to distribute oxygen throughout your body.