My layover will be in London Heathrow at 10am from Lax Los Angeles,my next flight to Rome will be at 12:45pm..is that plenty of time to catch the second flight? I'll be only taking a carry on bag NO check bags
Lots of time. You will be fine.
Check if your London arrival terminal and departure terminals are the same. If they are, it's easy and you should have extra time. If you have to change terminals, find out how to do that before you go (see the Heathrow website). You will still have time, but it will reduce your stress level. If your arrival is significantly delayed (especially if you have to change terminals), first ask the flight crew on your plane what to do. Often the airline makes arrangements since there are likely to be many passengers with connections). Otherwise ask the airport officials on the ground if it's possible to expedite your transfer (like jumping line at security) - there may be a separate line for short connections, for example. This is not likely to happen, but it's better to be prepared.
Yes its all going to be in the same terminal,thanks for the info