Kudlow is 70 years old and joined the administration in March. The president tweeted that Kudlow is now at Walter Reed Medical Center.
Kudlow had worked as a White House budget aide in the Reagan administration, and had also been an informal advisor to the 2016 Trump campaign. While he had the backing of Treasury Secretary Steve Mnuchin, he was ultimately overruled by Robert Lighthizer, the US trade representative.
But since joining the Trump administration, he has faithfully executed his boss's agenda - arguing for instance that the European Union must make "concessions" if it wishes to be exempt from tariffs, and signalling the U.S. is prepared to walk away from two-decade-old North American Free Trade Agreement. The Canadian government immediately rejected the idea.
"POTUS is not going to let a Canadian prime minister push him around", he said.
Trump tweeted just minutes before his historic meeting with North Korean leader Kim Jong Un that Kudlow is being treated at Walter Reed Medical Center.
Kudlow's heart attack came less than three months after Trump tapped the former CNBC host and commentator to chair the White House's National Economic Council.