Mike Bloomberg and Bernie Sanders' presidential campaigns sparred Wednesday over which 78-year-old is in better cardiac health.

The big picture: The line of attack comes as Sanders, the race's current frontrunner, is set to meet Bloomberg, who has spent hundreds of millions of dollars to make a splash in the race, face-to-face for the first time on the debate stage in Nevada.

The state of play: Sanders' national press secretary Briahna Joy Gray told CNN that Bloomberg "has suffered heart attacks in the past."

Bloomberg senior adviser Tim O'Brien hit back on Twitter, calling the statement "a Trumpy lie from the Sanders campaign, which rolls like Trump in many ways."

Bloomberg released a letter from his doctor last year, which featured no mention of a heart attack but did note that he underwent coronary stent placement surgery in 2000.

Bloomberg campaign manager Kevin Sheekey said in a statement that the surgery occurred after a positive stress test and has been "public for years" since Bloomberg, who holds a pilot's license, had to inform the FAA when it occurred.

Gray later walked back her statement about Bloomberg on Twitter, stating that she "misspoke" and that he "underwent the same stent procedure as Bernie."

The other side: Sanders suffered a heart attack last October that briefly sidelined him from the campaign trail.

The Vermont senator released letters from his primary physician and two cardiologists late last year stating that he "has the mental and physical stamina to fully undertake the rigors of the presidency."

Sanders said this week that he was unlikely to disclose any additional medical information, stating that he has already put forth "quite as much as any other candidate has," reports The Hill.

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