The Japanese word for heart is
心臓

しんぞう - shinzou
心-heart, 臓-organ

heart

Japanese Definition

heart
1. 名詞. 心臓、心こころ
In Sylvester Stallone's famous movie Lock Up, Frank Leone has a heart of gold.
2. 名詞. ♥：心臓を象った記号。ハート型。
3. 名詞. ハート。トランプのスートのひとつ。
4. 名詞. 本質。核心。

心臓
1. n. (anatomy) a heart

中心
1. n. center, middle, heart, core (physical center)
2. n. center, hub (most important area of activity)
3. n. crux, main point

気持ち
1. n. a feeling, sensation, feelings
(ja-x, 気持ちがいい, きもちがい.い, to feel good)
2. n. a state of mind, mood
3. n. mood of a place; atmosphere
4. n. feeling depending on a physical condition
5. n. a little, a bit

ハート
1. n. (anatomy cardiology) (syn of ja, 心臓, tr=shinzō, , heart)
2. n. (syn of ja, 心, tr=kokoro, , heart) (emotions or kindness)
3. n. (cards) hearts
4. n. Usage: For the organ sense, the term 心臓 is more common. For the emotional sense, the term 心 is more common.

心
1. n. mind, heart, spirit, soul; thoughts, ideas
心の底から - from the bottom of one's heart
人の心を奪う - to steal someone's heart → to captivate someone
2. n. attention, mind, interest
心ここにあらず - absent minded
3. n. heart, feelings, emotion, emotional state
心温まる風景 - a heart warming situation
4. n. wholeheartedness, sincerity, true heart
心のこもっていない - not sincere
心のこもった - sincere
心なき仕業 - cruel deed
5. n. sympathy, heart, consideration, generous disposition
心がない - lacking sympathy and consideration
6. n. a meaning, essence
その心が分かっていない - not understanding what it really means
7. n. an answer (gl-lite, to a riddle, etc.)
その心は - the answer is
8. n. the heart as an organ in the body
9. n. the chest
10. n. the title of a book
11. n. a heart, inner feelings
12. prefix. (expresses heartfelt feeling)
13. n. a heart, mind, core
14. n. a spirit, vitality
15. n. inner strength, marrow
16. n. the center of something:
17. n. 心, 芯: the core (gl-lite, for example, of a fruit)
18. n. 心, 芯: a wick
19. n. (Buddhism) citta: the ego or spirit
20. n. the heart as an organ in the body
21. n. lead (gl-lite, as of a pencil)
22. n. padding
23. n. a companion, fellow
24. n. the center of focus:
25. n. the important part
26. n. a basis, foundation