The bidding goes
Pass - Pass - 1D - Pass
1H - Pass - 2H - Pass
2S! - Pass - 3H All Pass
2S was an artificial bid asking partner to bid the cheapest suit in which he would accept a game try. 3H said that partner wouldnt accept any game try.
You have the agreement that partner can raise to 2H on 3-card support and shortness, but somehow you dont recall that ever happening. You can count on 4 card hearts sipport.

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