Apparently, while Bev's 81-year-old heart is strong, she tends to retain fluids, owing to her age and small size. That, plus the drastic decrease in her physical activity since she broke her hip in 2013. The fluid build-up prevents the left side of her heart from fully functioning. Shortness of breath, plus other complications, result.
She's in nursing home rehab right now, and while some of the aides are terrific, others aren't. The place has the usual moronic, corporate-dictated "get the patient up and moving" policy (hey, it's rehab), despite the fact that Bev is suffering a major sleep deficit right now. Since there's absolutely no coordination between the various folks who visit her room, no one got the "Do not disturb" memo. For Christ's sake, if the woman can't get any sleep, how can she perform the various exercises they want her to do? A bureaucracy is a dysfunctional organism wherein one limb has no clue what the other limb is doing (or not doing). It's all about checking off boxes.
Update: Bev reports that she's up to the rehab requirements, now that they've been explained to her. Things aren't as dire as I thought. Which is always a good thing.