Hi,

what an unhelpful nurse. Did she never bother to get you in touch with the cardiologist? I imagine he would know the most, so it would good to get in touch with him.
And/or definitely try your obgyn. There has to be some way around this, I would imagine! I'm certainly no cardiologist, but maybe if they knew he was trying to make a baby they would have given him something else that does the same thing?
Definitely pursue it and good luck!