The incident took place late last night (2013 GMT) shortly after take-off, before flight VS025 returned as a precaution, the airline said. There were 252 passengers and 15 crew on board the Airbus A340 aircraft.
A Virgin Atlantic crew member was recorded saying to Irish air traffic control that they had a "medical issue with one of the pilots after a laser incident after take-off".
"The safety of our crew and customers is our top priority and we apologise for any inconvenience to those on board," the airline said.
Scotland Yard tweeted: "Aircraft forced to return to Heathrow after being hit by a laser strike".
Virgin Atlantic said it was working with the authorities to identify the source of the laser.
There has been a surge in the number of reported laser attacks on aircraft in the UK in the last few years, according to Civil Aviation Authority figures. More than 1,300 incidents were reported in each of the four years from 2010 onwards, compared to only 20 in 2005.
The busy Heathrow airport itself reported 48 "laser incidents" between January and June last year, according to the Civil Aviation Authority.
