Well, not normal, but certainly not unheard of. After bypass surgery they leave a wire temporarily hanging out of the chest, attached to the heart, in case there are rhythm problems. Heart surgery is very traumatic for the organ and it just needs a little while to recover. It's great that his heart has gone from 10-36% though, in just a week.
I also had a-fib after surgery, and was told at least 30% of bypass patients require treatment to get the heart into proper rhythm. In my case, a drug (Amiodarone) fixed the problem. Although not associated with a-fib, my pacemaker needed a lot of fine-tuning after the procedure as well as my heart health improved enough for the need of new settings. It sounds like the procedure was a huge success for your husband as well, that's an impressive percentage improvement. As Ed34 mentioned, the heart went through a huge transition and needs both rest and exercise.
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