Caulfield horseman Ross McDonald's condition has improved but he remains in intensive care in a Melbourne hospital after heart surgery.

The 69-year-old underwent a planned operation on Monday to insert six stents around his heart but a complication arose, extending the length of the surgery to 13 hours.

McDonald's son and fellow Caulfield trainer Clinton said McDonald has started to communicate with doctors and his family.

"He's improving, it's probably another week until we are really satisfied that everything's gone well but at this stage he's progressing well," the younger McDonald told Racing Victoria.

"He's talking, so he is starting to get with it a bit, we are heading in the right direction for sure."

Clinton McDonald said his father would remain in intensive care for the immediate period before doctors decided the next move.