Have 7 hours at Heathrow between flights any ideas on what to do besides power walk the concourses to get rid of flight cramps? Jocko the Elder
Seven hours gives you just barely enough time to buy a one-day, zone 1-6 travelcard and take the tube to central London, walk around a bit, and take the tube back to LHR. Allow an hour each way.
Less rushed would be to take a taxi to Windsor, see the castle, and take a taxi back to LHR. Allow about 20 minutes each way.