Of course the lifestyle is different...any of these subspecialities of peds are. Think about it logically, how many 10 year olds have a cardiologist vs. how many 70 year olds have one...you can only survive in peds cardiology if you are one of the best and work in a top hospital, again think about it, if your ten year old kid is diagnosed with some rare condition you're not taking him to the local hospital, it's gonna be hopkins/mayo/etc. Other similar speciailities such peds oncology, etc are plagued by similar problems, a majority of patients in their field are much older...to be honest you'll make more and have a more fulfilling lifestyle just staying with peds and not specializing, but to each his own