A friend and I (MS2s) were talking about some of the procedures we had learned about in our Cards block and realized that we didn't really know which ones were considered difficult. Are there procedures that take years of practice to become proficient, akin to surgery, and not worth doing yourself if you haven't been doing them? For example, are there instances where interventional cardiologist A would refer a patient to interventional cardiologist B, because B was more skilled at that type of procedure than A (maybe peripheral stuff)?