Will you be able to have an MD-Ph.D If you want to become a cardiovascular surgeon?

It is not necessary. To become a cardiovascular surgeon, a physician must hold the Doctor of Osteopathic Medicine (D.O.) degree or the Doctor of Medicine (M.D.) degree, be a licensed physician, and complete specialized residency and fellowship training. A plain old DO or MD with the proper training in cardiovascular surgery (residency/fellowship) is what you need. The D.O./Ph.D. and M.D./Ph.D. dual degrees are more research-oriented.