Get some surgical skills experience through your local University open day / widening access programme. It'll help you decide whether you enjoy fiddling about with surgical instruments, show you whether you have a natural aptitude for it, and give you the opportunity to speak with a variety of surgeons (nothing against cardiac surgeons, they're just a slightly different genre than your average surgeon).
As a medical student you can join the surgical society, pick surgical SSMs and PBLs, and make the most of surgical opportunities which present themselves.
As others have already said, having seen a CABG is not a wise reason to narrow down your career choices just yet, but each clinical opportunity you have can help point you in the direction of something which you enjoy, are good at, and are suited to.