Jayden Hardowar is recovering from the condition, known as Pediatric Multi-System Inflammatory Syndrome, and could be released from the hospital as early as Monday.
His family said in April he went into cardiac arrest and was rushed to the hospital.
"We saw him there, we checked for a pulse, no pulse at all," Jayden's father said.
Jayden's older brother is a Boy Scout trained in CPR.
He performed the emergency lifesaving procedure on Jayden until the ambulance arrived.
At the hospital, he tested negative for COVID-19, but positive for the antibodies.
Governor Andrew Cuomo announced Sunday that New York is investigating at least 85 cases of the mysterious syndrome -- including five deaths -- in children possibly linked to coronavirus.
New York Health Commissioner Dr. Howard Zucker said he has a team of more than 30 people who are working with the CDC to evaluate the cases.
We weren't looking for this because these children didn't present with respiratory illnesses," Dr. Zucker said. "So, all of a sudden we hear about children with cardiac problems, inflammation of their blood vessels, we try to figure out what is happening here."
Also Sunday, Mayor Bill de Blasio said there are a total of 38 cases of suspected PMSIS in New York City.
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