open-heart surgery
US /ˌoʊ.pənˈhɑːrt ˌsɜːr.dʒər.i/
UK /ˌoʊ.pənˈhɑːrt ˌsɜːr.dʒər.i/

1.
a surgical operation in which the chest is opened and the heart is exposed to perform a procedure on the heart or its major blood vessels
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He underwent open-heart surgery to repair a damaged valve.
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Advances in medical technology have made open-heart surgery safer.