The decision to bid 4S depends on the treatment of the 3S bid. With all my regular partners, this is preemptive, maybe something like (Kxxx,xx,xxx,xxxx or Kxx,x,xxxx,xxxxx). In which case, pass is correct. With an advanced/expert partner would you expect a bit more of a subtle bid, e.g. 2H/3H as a cuebid.
We were red and responder had
Kxxx
xxxx
A
Kxxx
For me, this is a clear 3H bid.