There are multiple financially well-rewarded avenues in this specialty.
Like Novacek said, non-invasive people are paid fairly well too, and in a multiperson practice share the profits proportionally with those who do high value procedures.
But electrophysiologists are becoming as well paid or better paid than some interventionalists (starting salaries >500K in private practice, often, depending on the market area). and imaging folks have always done well in high volume markets where they can read a lot of echoes or nuclear studies (>300k very often).
But the real reason the do cardiology is because you love the physiology: the fact that what you hear in your stethoscope, and judge with your clinical skills makes a difference, sometimes in the immediate care of very sick folks.
And these skills are augmented, but not replaced, by the objective tests and procedures you're equipped to do as a cardiologist, i.e., echo, cath, ep studies. And then you're empowered to fix these things w/ PCI, ablation, pacers, ICDs...