Our experience through Heathrow is that you should leave yourself a 3 hour connect time. It was a confusing maze to get from our arrival gate to our departure gate, and the bags had to be screened again, even though you never leave the international terminal. My daughter's bag was flagged to be inspected, and the screener was in absolutely no rush to get through the line of bags that were stacked up waiting. She took everything out and looked at every item, then left it to us to put it all back in the suitcase. On our way back to the US, our plane sat on the Tarmac for an hour past our departure time, causing us a lot of stress, since this flight had only a 2-hour connection time. They gave us some brightly-colored cards at the gate and told us to hurry. This time there were people directing us through the maze, and we did make the connection, barely. Our luggage spent the night in London.