Heathrow handled a record 4.85 million passengers in February, up by 1% on the same month last year.
Adjusting for the fact that 2012 was a leap year, traffic was up 4.6%.
The rise was due in part to the merger of BA and BMI, which contributed to a 1.8% increase in the average number of seats per aircraft to 198.4 seats, and a 2.4 percentage point increase in load factor to 69.6%.
European traffic performed well, up 4.4%, with Italy up by 11.6%, Portugal 9%, Germany 8.2% but with Greece down by 7.4%.
Of the Bric economies, traffic was up 29.8% for China, 4.1% to India and 3.1% to Russia. The only reduction was an 8.3% drop in traffic with Brazil, resulting in an overall increase in Bric traffic of 5.1%.
Middle Eastern traffic rose by 6.2% but was down to North America (1.9%), Latin America (4.6%) and Africa (11.7%).
Chief executive Colin Matthews, said: “This month’s figures reflect larger, fuller aircraft being used at Heathrow, not the addition of new routes to emerging economies which are so vital to UK trade, jobs and economic growth.”