"Our Great Larry Kudlow, who has been working so hard on trade and the economy, has just suffered a heart attack. He is now in Walter Reed Medical Center," Trump wrote on Twitter, just minutes before a historic summit meeting with North Korean leader Kim Jong Un.
A longtime TV personality, Kudlow, 70, succeeded former Goldman Sachs president Gary Cohn who quit Trump's team in March in protest at the decision to slap steep US tariffs on imported steel and aluminum.
As a commentator, Kudlow had strongly backed Trump's moves to cut taxes and reduce business regulations but was openly critical toward the president's tariffs moves.
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 signaling the US is prepared to walk away from two-decade-old North American Free Trade Agreement.
He raised eyebrows on Sunday when he described Justin Trudeau as having "stabbed us in the back" at the Group of Seven summit after the Canadian leader said Trump's decision to invoke national security to justify US tariffs was "kind of insulting" to Canadian veterans.
Kudlow was appointed head of the National Economic Council in April.
A trained economist and historian, he nevertheless represented a departure from the scholarly types normally chosen to lead the body.
He is better known as a TV pundit, known for his bullish pro-trade ways and comical manner as a 25-year-veteran of business network CNBC.
Still, in 2007, just as the US housing bubble was about to burst, he reassured his audience that there would be no recession in the United States.
In the 1980s, he served as White House budget director under President Ronald Reagan and is still a champion of that era's conservative, supply-side economics, which calls for cutting taxes to boost growth -- an ideology the Trump administration has emphatically embraced.