钻 = to drill / bore through;
心 = heart. The image is a drill bit boring straight into your chest - visceral and instantly memorable. Most often heard in the collocations
钻心地痛 (piercing pain),
钻心地痒 (unbearable itch), and
钻心虫 (zuānxīnchóng, the rice / corn borer - an insect whose larvae burrow into stalks).
