Heather ended up having a second night in hospital; she carried on fibrillating on Wednesday so in the end they decided to use the electric defibrillator, with instant results. However, the hospital staff then went home, leaving her for another night. It looks like their medical expertise is not backed up by good communications; nobody knew what the previous people had done or said, the ward staff didn't know what the doctors had done, and so on.
She was told she could go this morning, so I picked her up and took her home at lunch time. I'm back at work, and hopefully she is lying in the sun reading, surrounded by cats.