Helguson joined Cardiff on a free transfer from Queens Park Rangers this week, and Mackay thinks that the Icelandic forward's experience will be crucial this season.
Mackay said: "He has scored at international level, won 50-plus caps for his country and netted a number of goals in the Premier League last season.
"We know exactly what we are getting and Heidar will help our younger players, on and off the pitch.
"I will only bring players in who will improve our squad and make a difference. Heidar fits the bill perfectly."
Helguson finished as QPR's top scorer last season with nine goals to help the Hoops maintain their Premier League status.