Are his feet and ankles swollen too? Sometimes edema can be caused by poor circulation. Have you mentioned this to his cardiologist? Has he eaten more salt that usual in the past day or so. Any difficulty breathing? Pain? Sitting more than normal for him?

Try having him move his arms, hands and fingers every hour by putting his arms over his head, opening and closing his hands to promote circulation. He can even add a walk around inside the house at the same time. If they stay swollen it would give you some peace of mind to give his cardiologist a call. Of course, if you feel it’s an emergency don’t hesitate to call sooner.