私の心の中
is the way to say 'in my heart' in the Japanese language. hope i have helped! :)
my heart
heart is kokoro
kuroikokoro
kuraikokoro
meinu
Mikazuki no kokoro
You may say 'kokoro kara,' which literally (and conveniently) means "from the heart."
心魂 Shinkon
Heart is Kokoro こころ
Japanese word "mune" is literally "chest". In context, though, it may mean "heart" in an emotional expression, such as in English we say "heavy heart" or "my heart leaped"
影の心 Kage no kokoro
失恋 Shitsuren