Briahna Joy Gray, Sanders' national press secretary, tweeted Wednesday that she misspoke about Bloomberg having a heart attack.
"I [misspoke] when I said Bloomberg had a heart attack. Rather, he underwent the same stent procedure as Bernie," she wrote. "Bernie released 3 detailed medical reports in December -- just like the other candidates."
Her comments came after a CNN interview in which she discussed questions about Sanders' health after he experienced a heart attack last year.
Bloomberg's campaign responded by calling her statement "completely false."
Bloomberg campaign manager Kevin Sheekey noted that Bloomberg did have two coronary stents put in after a stress test in 2000 and that this had previously been made public -- but he denied any heart attacks.
"The Bloomberg 2020 campaign released more information about his outstanding health soon after he entered the race," Sheekey said. "Here’s what we know about Sen. Sanders: In October 2019, he had a medical incident in Las Vegas. He didn’t tell the public for days and the full details have never been released."
On Tuesday, Gray had said she misspoke when she had said that Bloomberg faced dozens of "sexual assault" allegations.
"I misspoke and I am more than happy to correct it. It’s 64 sexual harassment allegations. My sincerest apologies," she said.
Gray also faced criticism for comparing attacks on Sanders to those against former President Barack Obama.
"Asking Sanders to release health records he promised to release is not remotely equal to birtherism. What an ignorant argument, Sanders HAD a heart attack," author Tim Wise tweeted. "Obama was NOT born in Kenya. One is true, the other false. The parallel is absurd and diminishes the racism of the latter."
Gray tweeted Wednesday: "Obama DID release his birth certificate. Bernie DID release his health records. Get the analogy?"
"You might have made a living explaining racism to white people, Tim, but trust that this Black woman who literally grew up in Kenya, gets it," she added.
Fox News' Ronn Blitzer contributed to this report.