Over the 3H you can bid either 4D or a takeout double "X" At the 4 level an overcall should have at least opening hand points (unlike at the 1 level). With the overcall you bid 4D. If on the other hand you decided to make a takeout double you would be saying to partner I have at least 3 cards in all the other suits partner bid your longest suit - a huge big lie, however its the only way to find the par 4S contract here (and your partner will always hate you if they have the club suit not the spades) - its your choice
Acol Bidding
Over the 3H you can bid either 4D or a takeout double "X" At the 4 level an overcall should have at least opening hand points (unlike at the 1 level). With the overcall you bid 4D. If on the other hand you decided to make a takeout double you would be saying to partner I have at least 3 cards in all the other suits partner bid your longest suit - a huge big lie, however its the only way to find the par 4S contract here (and your partner will always hate you if they have the club suit not the spades) - its your choice
Plan Before You Play
Dummy goes down. In a suit contract count your losers. Spades:1, Hearts:1, Diamonds:1, Clubs:1. with 4 losers you need to get rid of 1 loser to make your contract. The best idea looks to be to throw a losing heart on your long diamond suit.
The Play
Diamond lead, apply "The Rule of Eleven" and you know that East doesn't have the KD, play AD, then draw 1 round of trumps losing to the AS win the club return, ruff the KC return, draw the rest of the trumps, play the 9D to draw the KD, ruff the club return, play the rest of the diamonds discard the 4C the JH and 10H on diamond winners, and play AH and ruff your low heart. For 11 tricks
Comment
You won't find your 4S contract if you overcall diamonds . A 5D contract goes light whereas a 4S contract makes. See how oppositions pre-empt interrupts with your finding the best contract?
The above commentary is intended as a guideline only. As with any Bridge hand there are many ways to bid and play any hand.