Last month, the hub had 6.14m passengers pass through it. This is a 1.2 per cent rise over March and April from the same time last year, including the early Easter break.
There was also a boost in transfer passengers using the airport, which is critical to making long haul routes viable.
This helped passenger volumes to emerging markets increase.
Passengers to Mexico were up 13.1 per cent, and to China up 16 per cent.
As with Gatwick, which also announced a rise in passengers in April 2015, the figures will be seen in the context of the ongoing debate on aviation expansion.
Heathrow chief executive, John Holland-Kaye, said: “Expanding Heathrow delivers exactly what the UK economy needs – creating up to 180,000 new jobs and £211bn of economic benefit right across the country, growing exports by increasing trade routes to fast-growing markets and rebalancing growth across the whole of the UK.”