It's very good to be skeptical especially with a drug like this. If you are experiencing scary symptoms see a medical professional asap. My intention was to direct my post to people who might be experiencing similar things and making matters worse by panicking. My intentions are not to be argumentative with these folks. One poster had it right - doctors shouldn't even prescribe this shit. ADHD is relatively rare condition which is now being widely over diagnosed and over prescribed.
I am not a medical professional, but I know my system very well. What I know about hearts is that they don't get weak- they get blocked, clogged, and dangerous rhythms. A heart becomes damaged after a heart attack when part of it dies due to a blockage or arrythmia. It is safe to say once the drug is out of your body, and it didn't do bad things to you, you are probably in the clear. It is always better to verify your condition with a medical professional.
In my case I took 60mg over the course of the day combined with coffee and a couple of cigarettes. I knew I was panicking, but I couldn't get past the physical symptoms. Just know your limits and don't try to push them as we tend to do with drugs like this.