He played junior hockey for the Montreal Junior Royals from 1934-36 and then joined the senior team. He played for the Royals until 1941 except for one season (1937-38) with the Harringay Greyhounds in Great Britain. He was a member of the Razzle-Dazzle Line with Buddy O'Connor and Pete Morin. The three of them were called up to the Montreal Canadiens in 1941-42. Heffernan returned to the Royals until 1943-44 when he scored 28 goals for the Canadiens and won the Stanley Cup. That was to be his last NHL season. He played two more years with the Royals before reitirng in 1946.