I am currently a CA3 and matched into CT fellowship. Due to unforeseen circumstances, this additional year of training is now seeming more like a burden. Having gone through the match process I am aware that I essentially signed a contract. Does any one have any experience in backing out of fellowship before starting?
I know of a few people who backed out of doing a fellowship, for several different reasons (family illnesses, unexpected job, change in interests...). This is a really tough decision that you need to think carefully about, and I would speak with some of the faculty you trust at your home program for more specific and direct advice. Your program will (in all likelihood) support you through this (especially since there is still a few months before the start of fellowship allowing them to fill quickly - there are plenty of qualified applicants available), especially if you detail your reasoning. If you are staying at your home program you need to meet with all involved about this - your current residency PD as well as your fellowship PD assuming they are not the same. If it is at another institution, you are obligated to speak with the PD there as well out of professional courtesy. Fellowship programs know the opportunity cost to you of foregoing a year of attending wages is significant, so unlike residency they are more apt to be understanding.
That being said, if you go through with this you will, in effect, close off this subspecialty as an option for you completely. No one will be willing to take a shot on a guy who already backed out once - again, there are many qualified applicants and all spots (except the odd one or two) have filled the last few years.
Will it hurt getting a private practice job? Probably not (unless a group you are interested in has a need for hearts-trained graduates), since you don't really need to tell them about this in the application process. It is getting towards the later side for jobs starting in July/August so I would recommend contacting groups immediately if you want to go through with this.
There are many pros and cons (honestly, in my opinion as someone starting a cardiac fellowship in a few months there are more cons not knowing your specific situation) that I am sure others can touch on. Whatever you decide, be sure you seek the advice of others (online is a reasonable start, but this is a conversation that must be had face-to-face with faculty) and do not make and rash decisions - once you withdraw it will be a final move on your part.