Kerry’s first goal, which arrived in the 10th minute from Tomas Casey, settled their nerves and created a five-point gap from which they never looked back from.
Roscommon corner-forward Robbie Fallon was their sole source of resistance hitting all but two of their scores.
But Heffernan’s first goal in the 17th minute ensured Kerry led at the break, 2-8 to 0-4.
When he completed his hat-trick by the 51st minute, Heffernan made the game safe for the Kingdom.
“I was nervous beforehand because I was afraid that we might not turn up today and get involved in a battle,” said Kerry boss Seanie O’Shea.
“I feared the lads might think that beating Kildare in the semi-final was their All-Ireland but the lads were focused and the game went according to plan.”
Kerry had navigated the difficult half of the draw beating Meath and Kildare while Roscommon, trained by Ollie Canning of Galway fame, met weaker opponents in Donegal and Armagh.
“We trained very hard early on for the Tipperary and Cork Munster minor games and we got them fit. They then went back to their clubs and played a good bit of hurling and it worked well for us.
“This is where we belong. This is the Christy Ring Cup of minor hurling and a lot of these lads will go on hopefully and play senior with Kerry.”
Scorers for Kerry: R Heffernan 3-6 (5fs), Thomas Casey 1-1, M O’Leary, K Carmody, C Hussey 0-2 each, P McGrath, D Goulding, D Collins, B O’Leary 0-1 each.
Scorers for Roscommon: R Fallon 1-5 (1-4fs), C Kenny 0-2.
KERRY: J Wallace; TB McElligott, C Savage, K Hannafin; D Goulding, D Fitzell, Tommy Casey; D Collins, B O’Leary; M O’Leary, Thomas Casey, K Carmody; P McGrath, R Heffernan, C Hussey.
Subs: P O’Connor for McElligott (40), J Godley for Tommy Casey (45), Philip Lucid for Thomas Casey (48), D Carroll for Carmody (50), F Horgan for McGrath (54).
ROSCOMMON: K Kellehan; C Duignan, S Naughton, G McDermott; P Dolan, C Dolan, S McCormack; J Brennan, G Hendrick; T Mullen, A Donnelly, G Egan; R Fallon, L Kilcline, C Mulry.
Subs: G Downey for McCormack (ht), C Kenny for Henrick (45), P Joyce for McDermott (50).
Referee: S Hourigan (Limerick).