England coach Roy Hodgson has included three uncapped players in his squad for the friendly against the Republic of Ireland on June 7 and the Euro 2016 qualifier in Slovenia.
Austin scored 17 goals for QPR, but could not keep the west London club in the Barclays Premier League, while Vardy struck three times in his last nine games to help Leicester complete their unlikely escape from relegation.
Goalkeeper Heaton, meanwhile, has performed well for Burnley this term even though they were relegated from the top flight two weeks ago.
Hodgson at Wembley on Thursday: "I am pleased (Under-21 manager) Gareth (Southgate) has cleared up any doubts as to who would be available for the seniors and the Under-21s. I'm very pleased with the squad we've been able to put together here, I think it's a very strong squad.
"In particular I'm very pleased to welcome three people who haven't been with us before but who get the chance, to some extent because of the Under-21s, because quite often we've used some of those players in our squad and it's given them the opportunity.
"It is a good opportunity for them to come and show us what they can do, and I don't think anyone would deny them the right to be there because they have had good seasons with their clubs, often in difficult situations."
Goalkeepers: Green (QPR), Hart (Man City), Heaton (Burnley);
Midfielders: Barkley (Everton), Delph (Aston Villa), Henderson (Liverpool), Lallana (Liverpool), Mason (Tottenham), Milner (Man City), Sterling (Liverpool), Townsend (Tottenham), Walcott (Arsenal), Wilshere (Arsenal);