A hospital in Milton Keynes has cancelled some routine appointments and elective surgery next week because of the extreme heat warning.
The chief executive of Milton Keynes University Hospital said outpatient appointments would not go ahead on Monday and Tuesday.
Joe Harrison warned that frail patients travelling to the hospital in the hot weather would be put at increased risk.
Mr Harrison said on Twitter: "It has been extremely busy @MKHospital over the past week, with more patients than usual needing emergency care and significant pressure on our staff.
"As we go into the weekend, temperatures are forecast to rise up to 39C on Monday & Tuesday.
"We have taken the decision to stand down routine outpatient appointments and surgery on Monday and Tuesday because many of patients travelling to these appointments are frail and at increased risk, and due to the unpredictable nature of very high temperatures on demand for emergency care and on care environment.
"We will do all we can to keep wards and departments as cool as possible, but we know this will be a challenge given the very high outside temperature."
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