intracardiac

The story

1. Proto-Indo-European*h₁én
2. Proto-Indo-European*h₁énteros
3. Latin*interus
4. Latinintrā
5. Englishintra-
6. Proto-Indo-European*ḱerd-
7. Proto-Indo-European*ḱḗr
8. Proto-Indo-European*ḱr̥díyeh₂
9. Proto-Hellenic*kərdíyā
10. Ancient Greekκᾰρδῐ́ᾱ (kărdĭ́ā)
11. Ancient Greekκᾰρδῐᾰκός (kărdĭăkós)
12. Latincardiacus
13. Middle Frenchcardiaque
14. Englishcardiac
15. English todayintracardiac

From intra- + cardiac.