In order to defeat 4♣ you will need to make 4 defensive tricks and it seems partner will be more in charge than you. Leading a Spade which you both bid seems like a good idea but the Spade surely will only stand up for one round, and enough defensive tricks will not be generated, Therefore you will need to think again. Perhaps partner has control of the actual trump suit, or the ♥ Ace. With this in mind you could now generate a Heart ruff for yourself. With  all this in mind you decide to lead the ♥4.

Declarer wins the first trick in hand and plays a club. Partner takes his Ace and now kindly gives you a Heart ruff (playing the ♥8 back - maybe some sort of suit preference signal confirming the Spade Ace).

You take your ruff and now underlead your Spades making sure partner wins. Partner wins and kindly give you a second Heart ruff. and you have now taken the contract one off with your careful thoughtful defence. Without partner's disruptive  raise of  3♠ maybe the opponents would have found their more preferable making 4♥ contract.