Heart inflammation is a "very rare" side-effect of the Covid vaccines made by Pfizer and Moderna, according to regulators in Europe.
The European Medicines Agency said the side-effects were more common in younger men.
The medicines safety body said the benefits of Covid vaccines continue to far outweigh any risks.
But doctors and patients have been advised to be aware of the symptoms of heart inflammation.
These include chest pain, a feeling of breathlessness and a pounding or fluttering heartbeat. Anyone with these symptoms should see a doctor.
Two conditions were linked to the vaccines - inflammation of the heart muscle itself, known as myocarditis, and inflammation of the fluid-filled sac the heart sits in, known as pericarditis.
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