The heart is nothing to mess around with bro!!! It is the lifeline to your body. My guess you have been taking it for a long period of time without a break as it seems you may have built up a tolerance to it. How long have you been using it ? My advice to you would be to slowly ramp down to avoid the "crash" type feeling and come off for a while.
It got outlawed because those "crazy fuckin' bodybuilders found another thing that works". Anyway...I would start with 25mg then maybe increase to a comfortable level if needed. Everyone reacts different, so find out what works best for you.