2C. The Stayman convention works a treat here! Whatever partner responds you can pass. 2D is great, you have five. 2S is the dream response, hitting your 4-4 fit and 2H is fine too. Even if partner only has a four-card heart suit, your three small ones are potential tricks to ruff losing clubs  .

Double: Partner has passed so this action is for take out. You are playable in three suits so the double is the most flexible bid and allows partner to chose your best fit. But here south has a heart misfit and a club stack so can make an easy pass to collect a lucrative penalty defending 2C doubled.

South could have rebid 2NT to indicate 23-24 points and essentially balanced but has jumped to 3NT, so must be in the point range 25-27. You have a five card suit, two fast cards ♥A and ♣K (great for slams) and potentially useful intermediate cards, three tens. This makes the hand well worth a raise to 6NT. Well done Steven  in evaluating the 23 points and upgrading to 25-27, See how the solid diamond suit is worth six tricks and well worth a a couple of additional points.

Incidently 7♦  is not a bad contract., work out how you can make it  

West has made a double 4♠ jump rebid rather than just a 3♠ rebid. So the question is what do we expect them to hold? Given that the 3♠  jump rebid is a strong hand with a good six card suit then the jump to 4♠ must be even stronger probably with a seven card suit. The worry is diamonds but see how we have most of the big cards in hearts and clubs, so it must be extremely likely if not certain that partner has the diamonds under control. Given all this a raise to 6♠ or 4NT (RKC) looks a reasonable option here.

West held an expected ♦K and the slam was secure. In fact when all the norths lead ♥8 that was thirteen tricks but unfortunately only +710 to the E/W pairs.

You have fourteen points and an almost solid club suit so this makes the hand worth a lot more. See how the clubs are a great source of tricks and with the ♠A to boot, providing a guard in the opponents suit, a rebid of 2NT or even 3NT will  get the hand across to likely land you in the best contract. As it turns out the two ♣J, ♥J compliment the other hands suits for ten tricks in NT and a massive eleven tricks in ♣ contracts despite only a combined twenty four points.

Pass: The hand is balanced, and you only have a four-card suit. Partner is unlikely to have a suitable hand for game. Most of the time they will be 5-8 points. With the type of hand required to make 4♥ will need a raise to 3♥ (9-12 points) or a two-level response in a new suit (9+ points). As it is the 5-0 heart break jeopardises 2♥!

Note:  4-4 in the majors always open 1♥ because this allows partner to support hearts or respond 1♠ ​​​​​​​ either way a major suit fit will be located.

Take ♥A discarding a club and ruff your last heart. Then play ♦A and another ♦. East is now end played and either has to concede a ruff and discard or lead into ♣A♣Q. This line gives you that extra chance and even if it does not work you can still fall back on the club finesse to land your slam. Not bad odds .