Thousands of American teenagers may have suffered heart inflammation after getting a Covid jab, a study suggests.

Researchers found up to one in 7,000 boys aged 12 to 15 years old developed myocarditis after receiving the Pfizer vaccine.

The condition — which is mild for most but can cause a recurrent heart palpitation in rare cases — was most common after the second dose.

Researchers at the healthcare provider Kaiser Permanente reviewed 340 cases of myocarditis and pericarditis in hospitals across eight US states.

Myocarditis is when the heart muscle becomes inflamed, while pericarditis is when the lining of the heart becomes inflamed.

A total of 119 myocarditis cases were confirmed out of 3.4million people who got their second dose in the study.

Children or teenage boys aged 12 to 15 years old were most likely to suffer myocarditis after a second dose.

'Continued communication with patients and providers about risk for myocarditis and pericarditis after Covid vaccination...

Analysis carried out for the agency and published in April this year found the rates were up to one in 600 for boys aged 12 to 15 years after the second dose.

In severe cases, the inflammation can weaken the heart, cause an abnormal heartbeat, or even lead to death

This illustration shows normal heart muscle compared to inflamed heart muscle due