Newcastle's youngsters head to Heritage Park, home of Northern League Division One outfit Bishop Auckland, in high spirits following a five-goal thriller against their local rivals following Kyle Crossley's brace and Heffernan's header, the Irish defender's first goal at under-21 level since joining United last summer following his departure from AC Milan.
A representative of Republic of Ireland at under-19 level, the Cork-born centre-back reflected positively on his side's victory against their Black Cats counterparts, the young Magpies' first league away win of the 2023/24 campaign.
"Everyone's happy at the Academy," the 18-year-old defender told nufc.co.uk. "Even around the building, the chefs and cleaners were all delighted that we've come back with a good result and we're all buzzing off it.
"We knew before the game there was going to be some senior lads playing (for Sunderland) and we had a young squad so it shows our team spirit and quality, no matter what opposition we face, comes through and it was a great result against them. It definitely shows our character.
"We were together right until the end, grinding it out to get the result we wanted and I think we deserved the win. Although we were playing against older players with more experience, we showed we also have experience for such a young team and were able to hold on for three points.
"It was nice to win over in Sunderland and jump back on the bus home knowing you'd secured three points. Everyone was buzzing."
Heffernan, who has captained Newcastle's under-21 side on a number of occasions this term, expressed his delight in netting his maiden goal at second-string level.
The promising youngster, who netted twice in Newcastle's 2023/24 UEFA Youth League campaign, admitted scoring at second-string level was longly overdue for the teenager.
"It was actually a long time coming and I wanted to score in the league for so long," he explained. "I'd scored in the UEFA Youth League for the under-19s but I was so happy to get my first goal for the under-21s and especially against Sunderland.
"The derbies are always big games and, for me, I think I play my best in those type of matches. You play football for that reason, for the big occasions, and I love playing in those kind of games."
Attention quickly turns to another clash against North east opposition as Newcastle, currently seven points adrift of the top 16 spots, aim to enhance their hopes of qualification for the play-offs with an encouraging result against Boro's youngsters.
Heffernan, who made his senior debut for hometown club Cork City at the age of 16 in October 2021, is keen for United to build on their bright away form of late, aiming to extend their unbeaten run on the road to five competitive matches on Friday evening.
He added: "It feels like another local derby so we'll be going down there with the same attitude as we did for Sunderland, trying to win and play good football.
"Your away form matters massively and your season can be defined as a football team. It's good that we're starting to pick up points away from home.
"Our goal is trying to get into the top 16. We do have games in hand over teams around us and if we take it game by game, managing to get a good run of form together as we are currently doing, I don't see why we cannot achieve that target."
