I too had the heart/chest flutters. They would come and go with no rhyme or reason-mostly when I was just sitting and watching TV. I did not have the cramps but have experienced many other side effects. I had my Mirena removed 1 week ago and have not had one heart flutter, not one headache, not one backache, only slightly depressed last Saturday but not too bad. I did not have a lot of side effects at first, some of them got worse over the past 6 months (I had my Mirena for 3 1/2 years.) My husband would rather go without sex than live with me with all the side effects. Everyones bodies are different though so maybe your body would get used to it? I would definetly tell your doctor about it though and don't accept the "It can't be the Mirena" because it very well could be.