A.T. Robertson Commentary Acts 2:37

"Now when they heard [this,] they were pricked in their heart, and said unto Peter and the rest of the apostles, Brethren, what shall we do?" — Acts 2:37 (ASV)

They were pricked in their heart (κατενυγησαν την καρδιαν). Second aorist indicative of κατανυσσω, a rare verb (LXX) to pierce, to sting sharply, to stun, to smite. Homer used it of horses dinting the earth with their hoofs. The substantive κατανυξις occurs in Ro 11:8. Here only in the N.T. It is followed here by the accusative of the part affected, the heart.

What shall we do? (Τ ποιησωμεν). Deliberative subjunctive first aorist active. The sermon went home, they felt the sting of Peter's words, compunction (χομπυνγο). Codex Bezae adds: "Show us."