I've been taking levoxyl for 8 years now with mostly good success...

I also have recently had my dosage of Levoxyl increased - I have been taking it for about 10 years now with absolutely now problems until now. I went from .125 to .150 and have been experiencing racing heart, clammy and short of breath. My Dr sent me to cardiologist because there is major heart disease in my family and I had a stress test and all was normal. As I am typing this I feel like my heart is going to jump out of my chest and I decided to look up if this is a side effect of Levoxyl. Doctor tells me my levels are good now with the new dosage but what is the best, the symptoms from the increased dosage of levels being off?