Depends what you mean by "academic"? Very little if any occurs outside of major pediatrics referral centers because a lot of resources are necessary to have a peds cardiac program. Some big referral centers don't necessarily have an attached medical school, but still have major NICU, PICU, peds intensivists, peds cardiologists etc necessarily to support a congenital heart surgery program
The short answer is that it's pretty competitive.
People who say anyone with a pulse can get in are a little bit out of touch. It's not competitive in the sense that you need >250 on step 1 or honors, etc. etc. to get into the field, it's a little more Consider this... look at the match outcomes for the thoracic surgery match for the last few years. I'm not super familiar with the congenital match, but there always seem to be more applicants than spots (and this is AFTER you've done 4 years of medical school, 5-7 years of residency and another 2-3 years of thoracic residency). To me, any field that it takes at least 11 years of high performance just to be qualified to apply to is competitive on principle alone. And then take into account that its a small field and there are a limited number of jobs out there. Finally, consider that once you finish training and finally have a job, if your outcomes are not very good, you won't have that job for very long. It is true that the training is long and that filters out a lot of people who choose to go into it, but that doesn't mean it is not competitive.
And yes, the technical skill needed in peds cardiac surgery really matters. Again, if you are not very good at performing the cases, you will not have a job for long. (This actually applies to all of CT/thoracic surgery)