splitimage, maybe they just want to try dropping your Effexor dose a bit to see if that helps, as a way of diagnosing whether it is the Effexor that is causing the problem. If dropping the dose doesn't help your heart rate, then they would move on to their next idea, e.g. their Naltrexone, and test that. (How high is your heart rate?) Hope they can figue it out and you can stay on the meds that are working for you.