Yes, this happened to me, you are definately not alone with the rapid heart rate. It is from the Mirena, and will get better with time. For me, I would be just sitting somewhere thinging about nothing and wham, my heart would start racing, hands shaking and sweating, short of breath, feeling like I was going to die. I likened it to a panic attack, even though I had nothing to panic about. I am a very laid back person. Then once I had Mirena out, often I would be sitting there and notice my heart beating very quickly. I can't count the number of times I'd be sitting at my desk with my fingers on my neck watching the clock to measure my heart rate. Right before I had Mirena out, the ER doctor I saw when I had a big "panic attack" perscribed a low dose of atenolol, which is a beta blocker. That helped slow my heart rate and calm me down, until I didn't need as much over time and I weaned off of it slowly. That was about the one year post-removal mark for me. I also bought a blood pressure monitor at the drug store, and that helped reassure me that I was ok when I felt my heart rate was too high.
Hope this helps. I know it sucks, but it WILL get better with time.
Peace,
nile

Yes,

I still get the feeling of my heart beating fast. Sometimes it's not, but it feels like my HR and breathing don't match up. When I ride my mountain bike my HR easily goes up to 170-180s which isn't right. I remember last year before I got the Mirena out I would ride my bike and my HR would go over 200. That is definitely not right. I'm pretty sure the Mirena did something to my vasculature. I put off going to a cardiologist because over the past year things seemed to be getting better (my heart palps pretty much went away). Now sometimes I feel like I forget to breathe. Anyway, I can't ignore these symptoms anymore and I have an appt. on Friday.