I really don't know the salaries for red peds cardiologist vs interventional.
I can tell you that I saw what the new faculty were being offered in teh dept of peds cardiology ( at the place where I did my fellowship ) and it was rediculously low ( but academic medicine often pays a fraction of what you can make in private practice )
In a big city, you just don't need that many peds cardiologist s in private practice, so most jobs are in teh academic setting.
Just something else to consider prior to starting.
and yes, many defects can be repaired nonsurgically, such as many ASD's and PDA's in older children.
Also valvuloplasty...like dilation of pulmonary valvular stenosis