"One Hand, One Heart" is a song from the musical West Side Story by Leonard Bernstein and Stephen Sondheim.
The original tune comprised just a single dotted note per bar, which Sondheim was loath to write lyrics for, as he would have to write all single syllable words, so he wrote lyrics making fun of the tune to persuade Bernstein to give him the extra notes.
... As in "Somewhere" the tune hamstrings the lyricist by virtually precluding the use of any two-syllable words, which sound ridiculous when stretched out so slowly.
But Lenny was very fond of the melody and wanted to use it for the Balcony Scene, so I asked him merely to give me a couple extra quarter-notes per bar, which didn't change the melodic outline.
This motif – which it must be remembered alludes to Tony's desire to get in on with Maria, and which therefore constitutes a social transgression which works to move the plot along to end tragically – symbolically suggests that their wedding will not take place because 'it shouldn't happen'.