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.
More top news
Andrea Byrne presents the first episode of the new series Helimeds which follows the Welsh flying medics.
Variable cloud and clear spells overnight with isolated showers mainly in the north.
Becoming drier and brighter from the northwest during the day, but with the risk of scattered, locally heavy, showers developing later.