With his bidding partner showed 5=3=1=4 or 5=3=0=5 and 15 HCP.
With his 3C bid he showed GF hand. If he had bid 3H iso 3C then that would have been 4 card H and GF.
His 4H shows a minimum hand, with more he can bid 3H.
Pass or 4NT (or anything else)?

Help

1S-2H
3C-3D
4H