heartstrings

noun[usually plural]4

1. •
   (historical) The tendons or other structures resembling cords once thought to be attached to, or to brace, the heart; especially the aorta, pulmonary artery, and other large arteries connected to them; also, the diaphragm.

   • Harte strynges uenies de cuevr. — 1530
2. •
   (figurative) The source of one's deepest emotions or inner feelings, especially compassion or love.

   • The sad eyes of the orphan tugged at my heartstrings.
3. •
   Synonym of chordae tendineae (“the cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart”).
4. •
   (figurative, no longer used) The essential or vital part of something; the core, the essence, the heart.