I think the definitions are slightly gray. But to me a "non-interventionalist" would be someone qualified in most diagnostic procedures and medical treatments. Thus he could be a master of reading ECG's and echograms, administering and interpreting stresss tests, both nuclear and non-nuclear. He might be a good man to help control BP and blood lipid levels and monitor a heart healthy diet.
The next step MIGHT be either one: a catheter angiogram. I think some might term the percutaneous (artery snaking procedure as either.)
Then broadly 2 areas of interventionalist:
1. angioplasty and stent placement,
2. open heart procedures like bypass.
Probably some would divide them into just 2 groups: Heart Bypass and everybody else.
Definitions aside, find out what you'd PROBABLY like done and choose the appropriate cardiologist. I very much DID NOT want bypass so I chose a man with a superb record (best in NYC) at angioplasty and angiography who didn't do bypass.
I think as a bare minimum, a cardiologist who does angioplasty is about right. Less qualified than that might mean being handed from one to the other...always unpleasant for the patient...US!
Don't be afraid to tell your GP that a referral to such a doctor is an absolute necessity. You are the one footing the bills.
If for some reason, you'd like to go the bypass route

, then pick a cardiologist who ONLY does bypassses...dollars to donuts, a bypass is what you'll get.