Have avg of 20k PVCs a day all tests are normal (Echo, etc). Beta blockers don't work. EP wants to try Diltiazem. How will this drug help with PVCs?

Less than 1 per hour. Annoying but probably not serious. BP normal? Get enough sleep. Do not smoke. Avoid stimulants and street drugs. Drug treatment of VPB is often ineffective.
Cardiology evaluatio. You may need to have a cardiology evaluation by an electro physiologist. If you are not responding to the therapy, your physician would have you see a cardiologist and the cardiologist would raise you to a electrophysiology evaluation.
It's a CCB. Many channels for rhythm in heart. Beta blockers didn't work Next he is trying calcium channel blocker ( diltiazem ) If this doesn't work there are many other drugs. It with increasing frequency of side effects. BB's and CCB's have safer side effect profile. .