Your doctor is probably following the ACC/AHA guidelines for non cardiac surgery, which dictate that for some patients with a moderate risk of death or myocardial infarction from surgery, and who undergo at least a moderate risk procedure ( yours is a low risk procedure), benefit from peri-operative beta blockers. No reference to cardiazem, which although slows down the heart is a calcium channel blocker. Hence he was simply trying to protect you from perioperative death or myocardial infarction by adding beta blockers to your regiment, which already included the cardiazem.
Some cardiologist would say that with an asymptomatic patient at low risk for any morbidity from non cardiac surgery undergoing a low risk procedure would not warrant anything but perioperative beta blockers.
I forgot to add that I am a 27 year old female otherwise in pretty good health. I also have rheumatoid arthritis and have had two episodes of pericarditis, which was extremely scary. Would the surgery increase the risk of pericarditis occurring again?