I've heard that those wands can mess with your heart rhythm if they're used near your chest area but I've never found confirmation of this. If you're heart is racing after using it near your chest maybe keep it away from that area until you can find out more.
When you say "heart racing" to what degree are we talking? Like heart palpitations? I mean, you're hearts going to beat pretty fast when having sex or pleasuring yourself as a rule, and orgasm is going to make it beat harder, but if you're having chest pains or palpitations, I would stop right away and talk to a doctor.