His son, Crown Prince Haakon, will serve as regent while his father is in hospital and convalescing, a period that could be as long as two months, Aftenposten reported.
King Harald suffers from aortic stenosis, a condition that tends to get worse with age. During the surgery, doctors will correct a defective heart valve.
The king was treated for cancer in 2003.
Charlize Theron not engaged to Sean Penn 'yet'
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend