Sen. Bernie Sanders suffered chest discomfort during a campaign event on Tuesday and underwent emergency surgery.

The 2020 candidate had two stents inserted to address a blockage in an artery, his campaign announced.

“During a campaign event yesterday evening, Sen. Sanders experienced some chest discomfort. Following medical evaluation and testing he was found to have a blockage in one artery and two stents were successfully inserted,” said Sanders’ senior adviser Jeff Weaver on Wednesday in a statement.

Sanders, 78, remains hospitalized in Las Vegas, Nevada.

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“Sen. Sanders is conversing and in good spirits. He will be resting up over the next few days,” Weaver said. “We are canceling his events and appearances until further notice, and we will continue to provide appropriate updates.”

“The Sanders campaign had planned to go on air with his first television ads of the campaign this week in Iowa, announcing a two-week $1.3 million buy on Tuesday,” the New York Times. “An ad tracking service, Medium Buying, said on Wednesday that Mr. Sanders began cancelling those ads. The reason for the cancellation was not immediately known. Even as late as Tuesday night, Faiz Shakir, Mr. Sanders’s campaign manager, was talking excitedly about the ad buy on a call with supporters.”

Sanders’ campaign released its first television campaign advertisement Tuesday morning.

“Defeating Trump is not enough. We need leadership that will fight for working families and the shrinking middle class, not just the one percent,” Sanders wrote on Twitter. “That is exactly what I have done my whole life and what I am prepared to do as president.”

Titled “Fights for Us,” the ad depicts the Vermont socialist as best able to defeat Trump.

“Bernie Sanders, fighting to raise wages for American workers, leading the fight for guaranteed health care for all, standing up for civil rights, seniors, veterans, and our children’s future,” a narrator says. “Whether it was Wall Street, the drug companies, or other powerful special interests, Bernie has taken them on for us.”

“Now our country is at a turning point. A dangerous demagogue tearing our nation apart, hardworking people betrayed by Trump, a health care system that makes enormous profits for drug and insurance companies, and a planet on the brink of a climate disaster. In this moment we need a fighter,” the narrator says.

“Bernie Sanders, we know he will fight for us as president because he always has,” the ad ends.