Yes there is a possibility that harm will come to your baby. To suggest such a procedure while so early in pregnancy must be because they feel you are at great risk with your heart. I would ask about the risks, and I assume they KNOW you are pregnant? In most cases angiography will be refused if you are pregnant. I believe the chemicals used pass through the placenta, which means they will enter your child and possibly cause deformities.
You better check with your doctors, I am not sure about the potential damage due to the radiation dose that you will take during the procedure.
Also if they discover blockages in your coronaries, I do not know about the risk of the medication that you will need.
Jesus