Crossword Genius

Uncle Sam's heart lacking constant record (5)

Ross

I believe the answer is:

enter

'record' is the definition.
(enter can mean to enter into a record)

I don't understand how the remainder of the clue works.

(Other definitions for enter that I've seen before include "A key on the right" , "Pierce" , "Join (for the first time)" , "submit?" , "Go/come in" .)

I've seen this clue in The Times.
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