It saw an additional one million passengers compared with the same period in the first half of 2019, before the coronavirus pandemic lockdowns.
Among the popular holiday destinations from the west London airport last month were Spain, Greece, Italy and Turkey, Heathrow said.
Additionally, the Taylor Swift concerts brought in an extra 40,000 passengers this summer, with fans travelling for her European Eras Tour shows, Heathrow said.
Chief executive Thomas Woldbye said he was grateful to staff their “preparation and dedication to delivering an extraordinary getaway for more passengers than ever before, maintaining strong service levels during what has been our busiest summer”.
“For the past four months we have broken several new records, demonstrating our ability to open a world of opportunity for more people, cargo, business and the UK economy.”
Manchester Airports Group (MAG) – which owns and operates Manchester, Stansted and East Midlands Airports – said it had also had a record-breaking summer.
Passenger numbers across its airports reached nearly seven million in August, up 6.6% from the same month in 2023.
Manchester and Stansted airports had their busiest ever months in August, with 3.4 million and 3.1 million passengers respectively.