Heathrow bosses have confirmed the airport accommodated 5.9 million passengers in March 2013 - a record for the month.
This was a 3.9 per cent increase on the corresponding month in 2012 and airport chiefs believe the integration of bmi into the British Airways network was the main driver of the improved performance.
However, slow global trading meant that the London-based aviation facility's air cargo traffic was down by 2.3 per cent during the month.
News of the impressive passenger figures comes in the same week that the facility scooped two accolades at the Skytrax World Airport Awards.
It was named 'Best Airport for Shopping' for the fourth time and Terminal 5 was hailed the 'Best Airport Terminal', much to the delight of Fidel Lopez, Heathrow's commercial director, who added that even more retail opportunities will arise when Terminal 2 opens next year.
Meanwhile, Heathrow chief executive Colin Matthews said: "We will continue to improve Heathrow for passengers and airlines, opening the brand new Terminal 2 in summer 2014. We plan a further £3 billion of investment over the next five years."