From Heathrow Terminals 1-3 train to London Paddington then train to Cardiff Central. 2 h 40 min £97. From Heathrow Airport London bus to Cardiff Coach Station. 3 h £32. From Heathrow Central Bus Station bus to West Drayton, train to Reading, then train to Cardiff Central. 3 h 6 min £66. From London Heathrow Airport (LHR) drive to Cardiff. 2 h 17 min £27.