How do you say "My heart is beating" in japanese (in romaji and in hiragana/kanji) ?
(in romaji and in hiragana/kanji)

Question

Answer

It may differ depending on the situation. Direct translation would be...
私の心臓はドキドキorバクバクしています。
Watashi no shinzou ha dokidoki(bakubaku) shite imasu.

If that happens when you see someone you like, you would like to use ドキドキ.

Answer

胸がどきどきする
mune ga do ki do ki su ru

Answer

I don't think Japanese have a heartbeat.  I have heard that they're all zombies.

Answer

In a sentimental way, like when you see someone you like or you are anxious about something you say: 心がドキドキする。Kokoro ga doki doki suru.

In a physiological way you say:
心臓が鼓動する。 Shinzou ga kodou suru.

Answer

Japanese: "胸(or心臓)がドキドキする。"
Romaji : "Mune(Shinzou) ga dokidoki suru."
Katakana: ムネ(シンゾウ)ガドキドキスル。
Hiragana: むね(しんぞう)がどきどきする。