I've never felt similar thing in my VILD attempts, which have been quite a lot lately.
So I'm just assuming that this accelerated heart rate could be that you're anxious about LD'ing, and somewhat stressing for the technique to work.
This may be why I never experienced it - don't stress about it, but don't ignore it either, just be aware of what you're doing and why you're doing it but don't stress too much over it.. It's a little hard to put it to words, but I hope it was helpful.