Hart had a spell out of the Manchester City side last season following some underwhelming performances but he re-established himself as first choice as City clinched the Premier League title.
The 27-year-old is now looking forward to England’s World Cup opener against Italy in Manaus on Saturday but he is also aware of the threat to his place from Ben Foster and Fraser Forster.
He said: "I am really enjoying what I am doing and really enjoy the opportunities that are coming my way.
"I am well aware that can change really quickly as I am with two sides, they can pick from any goalkeeper they want.
"England have got an amazing array of goalkeepers. We've got two here alongside me, who I think any team around the world would want.
"Obviously at Manchester City they are capable of buying or bringing in whoever they want, whoever they need to.
"I've got to be at my best, I've got to be working hard and you've got to stay level-headed otherwise it can go wrong.
"Ben is a fantastic goalkeeper and we're really lucky that, as a unit, we've got a lot of respect for each other on and off the field.
"He has been absolutely fantastic since he's come back in, a real breath of fresh air, and the same goes for Frase as well. We work well as a group. We get the best out of each other and want the best for each other.
"If Ben was to play, he would have my utmost support and I would want him to do well.
"I think we're doing a lot for each other. We are working hard as a unit. We have a lot of support for each other and have a lot of respect for each other.
"I think it helps that we like each other on a personal basis as well as a football basis. I've got a good relationship with the goalkeeping coach and we're just trying to get the best out of each other.
"We realise what an opportunity this is. They don't come around all the time but, like I say, we're just trying to get the best from it and I think the best way of doing that is to work hard and work well as a team."