She had an embolism of some type (I'm sure the words embolism and thrombosis were in there... you'd think I'd be able to recognise the terms after my years of medical-drama watching!)--basically a clot broke free and lodged near her shoulder.
The prognosis for her leg is poor--it's likely to stay paralysed, but as it's a front leg, this isn't too bad; I've seen many 3 legged animals who did just fine. Her overall outlook is better--we need to make sure she doesn't have a 2nd embolism, as that has a good chance of being crippling or fatal. So, weight loss and anticoagulant injections from now on. She'll see the regular vet again in a week, and the cardiologist in a few weeks when she's in (the cardiologist comes in once a month).
She's much more alert and is hopping around. She can move the leg a bit, but not walk on it.
The bill, by the way, was £1,200.
ETA: OK, a thrombosis is a clot that forms in a blood vessel, while an embolism is one that forms elsewhere and travels, so this was the latter and either he didn't mention a thrombosis at all or I mis-heard him (he's French, so it's possible). He's also looking into another anticoagulant so we don't have to give her injections twice a day. She's quite good with the shots but they are troublesome.
I also found a page on feline cardiomyopathy, which sounds like what Zoe has, and the information was depressing. By the time an embolism occurs, the heart muscle has sustained damage, and it can't be reversed. Congestive heart failure is a frequent outcome :-( Still, she's got beta-blockers and anticoagulants, and then again, plenty of people live a long time after being diagnosed with heart disease. She's not even 6 years old, so this is really sad :-(