Seems common to me, although with post-op open heart patients, I think it's a bit much. Where I work on my step down unit, we have post-op cath's (cardiac caths, carotids, peripherals, etc. with angio and stents), post-op pacemakers, ICU step down, drip patients (cardizem, dopamine/dobutamine, lido, amio, etc.), and neuro/cva patients. The only thing we don't have is open heart because our hospital doesn't have a cardio-thoracic OR. On day shift we go up to 5:1 (although realistically its more like 3/4:1) and on night shift we can do 6:1. We're a 29 bed unit, and we also get patient's from the med-surg units that flip into AFIB or SVT and need to go on drips.
Also, we have some staffing guidelines like no more than 2 drips in an assignment, if a nurse has a vented patient they have no more than 3 patients including the vent, and no more than 2 fresh post op cath's per nurse.