Abertawe Bro Morgannwg University Health Board says many of the people it has been treating have cardiac problems or have suffered a stroke. Many are over the age of 85.
The health board says it has brought in extra staff, and put on extra beds, to deal to with its A&E departments being exceptionally busy.
It says most routine operations have been postponed.
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Rain overnight turning light and patchy in the morning.
Most of us will have a pleasant and dry evening with a few late sunny spells, though the odd light shower is possible.
The Eisteddfod's intention to visit an area must be proclaimed at least a year and a day before the beginning of the festival.