If heart rhythms remain irregular for too long, it can trigger heart attack and stroke. 

Heart arrhythmias are a known and potentially life-threatening side effect of the malaria and lupus drug touted by Trump, so researchers in the US and France carefully monitored 90 and 40 patients, respectively, for them. 

Each found that more than 90 percent of coronavirus patients in ICUs showed longer-than-normal delays between heartbeats, a worrisome sign that the drug might be disrupting their cardiac function.