Caulfield trainer Ross McDonald is in intensive care in a Melbourne hospital after marathon heart surgery.

McDonald underwent a 13-hour operation to have six stents inserted on Monday but his son and fellow Caulfield trainer Clinton said complications arose during the procedure.

"It was a massive operation because they were going to do it in two parts but they planned it and did it all in one go," he said.

"The next 24 to 48 hours are crucial for him so we'll just see how he goes," McDonald said.

McDonald said it was business as usual at the family stable despite his father's operation.

Ross McDonald won seven Group One races with the brilliant galloper Weekend Hussler while he prepared Tristarc to win the 1985 Caulfield Cup.

He also trained the outstanding filly Courtza to win the Blue Diamond Stakes and Golden Slipper in 1989.