Last month saw the highest number of ambulance callouts for life-threatening conditions since records began, NHS England officials say.
There were more than 85,000 category one calls, for situations like cardiac arrests and people stopping breathing.
Nearly 30,000 patients waited more than 12 hours to be admitted to hospital.
The heatwave could have been one reason for increased demand, but experts say hospitals already face immense pressures.
Richard Murray, chief executive of The Kings Fund said the pressure on hospitals was also being felt right across the health and social care system.
He added: "At the end of July, 13,014 people were still in hospital beds despite being medically fit to be discharged, often due to a lack of available social care support. The challenges affecting the NHS cannot be solved without addressing the issues in social care."
According to the latest figures one six out of 10 patients faced delays in being discharged from hospital despite being ready to leave.
On average 12,900 patients a day spent more time in hospital in July than needed. This is a a 11% rise on the previous month.