heartstrings

Short definition from Wiktionary

Noun

1. 1
   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.
2. 2
   Synonym of chordae tendineae (“the cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart”).
3. 3
   The source of one's deepest emotions or inner feelings, especially compassion or love.
4. 4
   The essential or vital part of something; the core, the essence, the heart.