North will pass, though some will bid a weak 2♥ as they are NV.

If N passes, E and S will also pass.

West, with a poor 12HCPs (no fist round controls and Qx doubleton, what to do?

He meets the rule of 15 that is important in position 4. If HCPs and number of ♠ s = 15 or more bid, otherwise pass. If you bid 1♥ the risk is the opposition will win the bidding in ♠ s.

1NT with this balanced hand 5332 is probably best.

North may bid 2♥ , if not East will bid 2♥ as a transfer to ♠ s which will be the final contract and will make.

If N bids 2♥ East will bid 2♠ s.

Some Norths may bid a multi Landy showing ♥ s and a minor, in which case south will bid 3♣ pass or correct and N/S will find the optimal contract of 3♦