Slightly confused. I am not sure what you mean by a "London Travel Pass".
There is the "London Pass here: https://www.londonpass.com/
This offers discounts for some admission fees. As many places (including most museums) are free, the consensus on this website is that you have to be a very intensive tourist to save money with this pass.
There is a "Travelcard", which is one of the two options for paying for your transport in London.
A Travelcard is a pass for unlimited travel for one or more days. When you buy the card you specify the areas (zones) it is valid for.
The other option is an "Oystercard", which is a pre-paid card,. You pre-load it with money, and it deducts the correct fare for each trip. When you do a certain number of trips per day, it reaches a "cap" and all other trips that day are free. When it gets empty, you fill it up again. See here: https://visitorshop.tfl.gov.uk/
For most tourists, the Oystercard is the best option. You can get an Oystercard at any tube station, including Heathrow airport.
Which do you mean?