Now a days, we do not advise any surgery for fast heart beat and most of these cases can be handled by cardiologists with percutaeous techniques. This involves a small puncture in the groin under local anaesthesia and then one can study the conduction system of the heart. Thereafter, radio frequency based techniques can be used to destroy the additional pathways of electrical current. This is a very simple procedure in proper hands and most patients go home with in 48 hours. Some patients can be managed with medicines but it is not possible to prescribe medicines on the internet. Most patients under proper medical supervision can undergo pregnancy normally.
I advise you to take your fiance to a cardiologist who specialises in electrophysiology.