What would you bid in response to your partner's 1♥ opening bid?
You should bid 2♣.
Let's look at how awkward the auction gets if we bid 1♠ partner may respond 2♦. At that point conveying both our game forcing (mild slam try) strength and our heart fit becomes difficult. First we must set the game force with 3♣ (4th suit forcing). Partner might respond 3♠ or 3NT, leaving us with no option but to bid 4♥.
Or suppose partner raises 1♠ to 2♠, this is what we were hoping for when we bid 1♠ right? But maybe partner has something like:
If you play some convention, you can hopefully uncover if partner has 3 or 4 card support. If not, we are left with a guess. We can probably survive by bidding 4♥, but it will be tough to explore for slam without risking getting too high.
Now let us compare how easy the auction becomes if we start with 2♣.
Now we have forced to game, and shown our heart support while at the 2 level. Even if partner bids 2NT over 2♣ we can still show our heart support at the 3 level, and we have all of our other tools available, such as serious/non-serious 3NT, cue bids, and Roman Key Card.
We do not risk losing the spade suit as partner will always bid 2♠ with 4, and we can raise to 3♠. Again we have set trumps and established the game force at the 3 level, and still have our slam tools available.
While I may be in the minority, I believe it is even right to bid 2♣ on 4333, 42(43) and even 4342 (if you play 2♦ promises 5). 2♣ in essence, becomes either clubs or any balanced game force. If you are a fan of system, there are certainly ways to improve over the standard framework after 1♥-1♠, such as Gazilli which is popular with many of the Italian pairs, but that is another article.