Phil Goff is in hospital after undergoing unplanned cardiac surgery.
The Auckland Mayor underwent an angioplasty at Auckland Hospital on Saturday.
A spokesperson told Newshub he will remain in hospital for a couple of days, and will return to work in a week's time.
His Deputy Mayor, Bill Cashmore, will take over during that time.
An angioplasty is a minimally invasive surgery that widens narrowed or obstructed arteries. A medical balloon is inflated to open the artery and improve blood flow to the heart.
Mr Goff's predecessor Len Brown underwent major bypass surgery after suffering a heart attack in 2008.