Answer
You are South 3rd seat, favorable.
What’s your call? Because East is vulnerable against not, one option is to pass, hoping that partner re-opens with a double; you could pass and hope to score 500 or better (beating any game contract available for NS).
You could bid four diamonds (natural and forcing).
But if you decide not to pass (gambling for plus 500 or better), we favor a three notrump call. Likely, East has no entry outside of hearts, and with K54 you hope that you can hold up, exhausting West’s hearts. There are no guarantees, of course..
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