Industrial action by British Airways (BA) cabin staff meant Heathrow lost 180,000 passengers, according to BAA figures, and a further 20,000 at its other UK airports.
Despite the strike, 5.2 million passengers travelled through Heathrow in March, an increase of 0.4% on March 2009.
But BAA's UK airports as a whole saw a 1.5% decrease in passengers in March, compared to the same month in 2009, with a total of 8.2 million passengers.
"Without strikes it is estimated that Heathrow would have recorded a growth of 3.8% on last year, while the Group as a whole would have seen an increase of 1%," said BAA.
"Glasgow (down 9.6%), Edinburgh (down 3.3%) and Aberdeen (down 4.4%) were all affected by the British Airways industrial action, with each losing an estimated 1 to 2% of traffic for this reason."
Stansted airport, which was not affected by the strikes, also saw a decline in traffic of 4.2%, while Southampton grew 5.3%.
Colin Matthews, BAA's CEO, said: "There is no doubt that the market remains difficult, compounded by industrial action last month. Despite the industrial action, Heathrow continued to demonstrate the resilience which comes from its role as the UK's only hub airport."
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