Mackay's key signing as a professional was under Walker in 1952 (initially part-time whilst also working as a joiner). Mackay's pairing with Cumming at wing half was to become the nucleus of the team in the middle of the pitch. Mackay was a supremely talented all round player of ferocious tackling, endless running and sublime ball control. Cumming's "Iron Man" nickname says much of his fearless determination. Despite his commitment he retained control of his temper and was never booked in his career. Cumming was the only player to collect medals for all seven of the trophies Hearts won under Walker. "He never had a bad game. It was either a fairly good game or an excellent game," said Mackay later of his former teammate. Both went on to become full Scotland internationalists while playing for Hearts.