Sorry for the delay in response. As it were the last post occurred right as things were getting pretty busy for me, both at work and at home. I would concur that cardiologists have a fairly busy lifestyle at an academic center. Currently that is my only frame of reference. I would hazard a guess that someone at other types of practice might be less busy, but I'm unsure. Answering a question about call schedules for staff or fellow is somewhat difficult-it will be very program/practice dependent. For example (in regards to fellowships): I interviewed at three mid-size programs. One program had month-long rotations and (I vaguely recollect) you were on call q~5-7. Another had two-month long and you were on call for two-week blocks, rotating amongst the fellows. My program has two week rotations and you are on call three days a week while on the inpatient service, one day if on the cath service, and Fri-Sun rotates amongst all that are not on the inpatient service. A lot of programs are mostly home call (but call-ins can be fairly frequent) and some are a mix of home and in-house call. And there is certainly a variety of size in different programs (the largest being Texas Children's, Michigan, CHOP, and Boston and some mid-large programs like Atlanta Children's, etc).
If I were to give you a gestalt of "busiest" subspecialty lifestyles it would go something like this: PICU & NICU are going to be the busiest for obvious reasons. Of the specialties that have an outpatient component, Heme-Onc is probably the busiest with Endocrine, Cards, and Neurology coming in a close second. The nature of an individual program/practice may substantially affect that though. Depending on the practice GI docs can also be quite busy. The least busy would be Adolescent, and pediatric-focused allergists. Peds ED kind of has to fall into it's own category due to the shift work.