What should I bid after my opponent has opened the bidding?
I assume your opponent opened 1♣
I would double with your hand. “As an Overcaller all really good hands start with a double.”
After the double, your partner should cuebid the opponent’s suit by bidding 2♣. This is a common practice used to show a hand holding 12+ HCP, that isn’t sure either where to play or at what level. You’ll bid 3♥, showing long hearts, setting hearts as trumps and a hand that was too strong to simply overcall. 3♥, in this context, is a game forcing bid. Things get a little difficult at this point if you’re not familiar with more advanced concepts that established partnerships usually agree and discuss.
What should happen is that your partner will cuebid the ♠A and you will probably just bid 6♥
There is a bid that could be used to explore seven, called Exclusion Blackwood…..but that’s something that only high level players employ. Even they sometimes have problems with these auctions.