There were more people than ever before waiting for routine operations on the NHS in England - 4.4 million - in June.
The government target is for 92% of patients to start treatment within 18 weeks - but only 86.3% did, meaning 600,000 people had to wait longer.
In July, the number of people going to accident and emergency units in England hit a record high of 2.27 million.
NHS England says the heatwave was one factor - but overall demand also increased.
Top surgeons are calling for a five-year plan to clear the backlog of patients waiting for consultant-led hospital treatment, including more hospital beds across the country.
Prof Derek Alderson, president of the Royal College of Surgeons of England, said the number of patients "languishing on waiting lists remains at an utterly unacceptable level".
The number of people waiting for routine operations is the highest since modern records began, in 2007.
Waiting lists in England have been rising steadily for the past year, with June's figures a slight increase on May's.
Some hospitals say one factor in recent months has been the row over doctors' pension tax relief, which has seen some consultants reluctant to take on extra shifts to help clear the backlog of operations.
The government has now come up with new proposals to end the row.
An NHS official said staff had "pulled out all the stops" to deal with the record heat during July, treating more patients than ever before within four hours in A&E.
The previous highest number of A&E attendances, 2.17 million, was in July 2018.
Health think tank the Nuffield Trust said the figures showed "relentless pressure throughout the whole system".