I have been on prednisone before, and I also got severe tachycardia. I was not admitted to the hospital (though I should have been). I had some other symptoms with it- including severe dehabilitating leg cramps, shortness of breath, shooting chest pain. I found out later that I am generally allergic to all anti-inflammatories- which includes sterioids that are taken in by mouth or by blood. Since I have asthma, I have to be on a cortisteroid (that is inhaled)- Symbicort/ Pulmicort. I don't get any reaction to that. Usually if you have tachycardia, it is a sign of an allergic reaction. :) hope that helps!