That’s because myocarditis can lead to heart failure. When that happens, some people don’t get any advance warnings, which include chest discomfort, heart palpitations, shortness of breath, lightheadedness, swelling and fatigue. And the most serious outcome — sudden cardiac arrest — can also occur without symptoms. Before the pandemic, some 400,000 adults in the U.S. died of sudden cardiac arrest each year. It’s unclear how often myocarditis is the cause; estimates range from 1 percent over all to as many as 20 percent in young adults.
Even if myocarditis turns out to be a common feature of Covid, we won’t know how much it increases the total number of those affected by the condition. The definitive way to diagnose it is through a biopsy of heart tissue, but unless people show symptoms, they aren’t usually screened for myocarditis, which is typically caused by viruses, including influenza. When detected cases result in reduced cardiac function, about half the time the heart returns to normal on its own, even if scarring remains, according to Clyde Yancy, chief of the division of cardiology at the Northwestern University Feinberg School of Medicine and deputy editor of JAMA Cardiology. When it comes to cases caused