Go to the cardiology web sites in the hospitals near you or that you’re interested in, look at the providers and their profiles, most Dr profiles will have a section with clinical interests or research interests. For example the profile of my cardiologist says:
CLINICAL INTERESTS:
Adult Congenital Heart Disease
Bicuspid Aortic Valve
Thoracic Aortic Aneurysm
With that I know this Dr specializes in what I’m interested in. BTW in my case he truly is, my cardiologist is an aneurysm/aortic valve nerd which has been incredibly helpful (I had an ascending aortic aneurysm which was repaired and a bicuspid valve which will need replacing at some point in the future)