Bernie Sanders experienced chest discomfort during a campaign event Tuesday evening and had two stents inserted to address a blockage in an artery, his campaign announced.

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

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The Vermont lawmaker has kept up a relentless campaign schedule, particularly during the summer months, and often makes three or four stops a day in different regions. He was scheduled to attend a gun policy forum in Nevada on Wednesday, and then make seven appearances in California on Thursday and Friday.

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At 78, Sanders is the oldest candidate in the Democratic field. But he projects vigor belying his age on the trail, and has not been faced with questions regarding his stamina and mental acuity that have plagued former Vice President Joe Biden, who is two years younger.

The news of Sanders' procedure came as Advertising Analytics, an ad tracking firm, confirmed to POLITICO that his campaign had canceled its recently scheduled $1.3 million ad buy in Iowa on broadcast and cable television, which was announced Monday and set to begin Thursday. Mike Casca, a spokesman for Sanders, described the cancellation as "just a postponement" and did not elaborate.

Sanders on Tuesday posted a robust $25 million fundraising haul in the third quarter of the year, but has been eclipsed in recent primary polling by Elizabeth Warren.

"Bruce, Team Warren, and I are sending all our best wishes for a speedy recovery to @BernieSanders," Warren tweeted Wednesday. "I hope to see my friend back on the campaign trail very soon."