Newcastle's youngsters reported back for duty earlier this week before hard work, both on and off the pitch, got underway in preparation for the 2024/25 season.
Heffernan, who joined United last summer following his departure from AC Milan, was pleased to return to Tyneside after the summer break as well as reuniting with his Magpies teammates.
The Irish centre-back told newcastleunited.com: "I'm delighted to be back and being in that routine of playing football again. It's been good and it'll probably be a tough few weeks to come but I've enjoyed it so far.
"We've been doing a lot of tests, being in the gym and then out on the grass, getting back into our first session which is always nice in getting on the footballs.
"It's always nice coming back in and seeing familiar faces and we have a really strong bond as a team. There's also some lads who've signed their first professional contracts and they are all hungry to impress and earn their spot in the team.
"I think it's all healthy competition with everyone pushing each other on which is the most important thing."
Newcastle's youngsters rounded off the previous campaign with a piece of silverware after winning the Northumberland Senior Cup, defeating Blyth Town 2-1 in the final at St. James' Park.
Heffernan, a representative of Republic of Ireland at under-19 level, is keen for United's second-string to build on their positive conclusion heading into a new season.
The 19-year-old added: "Pre-season is key to getting as fit as possible going into the season, trying to get some minutes under my belt and getting as close to match fitness as I can. I wouldn't say it's my favourite time but you've got to do it. During the season, you then reap the rewards and that's why you put all the work in early.
"It was important for us to end the season on a high and, hopefully, we can now bring that energy into this season. Everybody is looking forward to it, whether we win the same trophy again or we look for more. We are all excited to getting the season started and seeing how we get on.
"Coming to a new club is always difficult but I think I settled in easily, playing so many games that I think I've learned so much from all of that and I'm ready to bring all of my experiences from last season into this one."
