I have been taking effexor for the last 3 months. I started on 75mg, increased to 150mg and am now taking 225mg. When I increased I experienced heart palpitations. I do get these with my anxiety but noticed that I was geting them when I wasn't anxious.
I had an ECG but it was normal. Palps are a common side effect and I found that after a couple of weeks they just dissappeared. I found that all the side effects I experienced from the effexor dissappeared after i had got used to it.
Now I am side effect free I have found this medication to be really good and it has helped my anxiety and depression so much.
I stuck with it but see how you feel. If you are having what I had, they will go away.