There has been one cancellation at Gatwick, while Southampton, Stansted and Edinburgh airports have told passengers to check for delays.
Drivers have been urged to take care and Wightlink Ferries have been suspended between Lymington, Hampshire, and Yarmouth, in the Isle of Wight.
A fog and ice warning covers Wales, the Midlands and southern England.
The Met Office yellow "be aware" warning is in force until Wednesday morning.
On Monday, Heathrow, London City, Gatwick and Southampton airport had cancellations.
Bournemouth Airport
Bristol Airport
Cardiff Airport
Gatwick Airport
Heathrow Airport
Luton Airport
London City Airport
Southampton Airport
Southend Airport
Stansted Airport
A Heathrow spokesman said "persistent freezing fog" had reduced visibility at the airport and said Tuesday's cancellations, made out of about 1,300 scheduled flights, were to allow for delays.
"With Heathrow operating at more than 99% capacity, there are no gaps in the schedule that can be used for delayed flights and as a result, some passengers may experience disruption to their journeys today," the spokesman said.
"As always, Heathrow's top priority is the safety of passengers and we apologise to those whose travel has been affected by today's weather."
A Gatwick spokeswoman said: "Air traffic control restrictions imposed due to fog across the South East and Europe may cause some delays to flights."
Road users have also been warned of difficult driving conditions after Dorset Police reported 31 collisions on Monday morning - six times more than would occur at that time on an average weekday.
The force has urged motorists to take extra care on Tuesday, while the Met Office warned journeys were likely to take longer than usual because of the adverse conditions.
Meanwhile, ferries running to and from the Isle of Wight between Lymington and Yarmouth have been suspended until mid-morning on Tuesday due to dense fog, Wightlink Ferries said.
It has advised customers booked on that route to re-book via Portsmouth and Fishbourne, and coaches will be provided for foot passengers hoping to travel on the alternative service.
Motoring organisation the AA advises:
BBC Travel
BBC Weather
Highways England
About 100 flights have been cancelled at London's Heathrow Airport for a second day because of fog.