あんなに平へい然ぜんと嘘うそをつくなんて、心しん臓ぞうに毛けが生はえている。
Lying so calmly like that, he must have nerves of steel.
彼かの女じょは心しん臓ぞうが強つよいから、批ひ判はんされても気きにしない。
She's thick-skinned, so she doesn't mind criticism.

Metaphorical use for the core or central part of a system, organization, or place. Common in compounds like 心臓部.

Usage patterns

心しん臓ぞうが高たか鳴なるone's heart pounds/races (from excitement or nervousness)
初はじめてのデートで心しん臓ぞうが高たか鳴なった。
My heart raced on my first date.
〈人ひと〉は心しん臓ぞうが強つよいsomeone has nerves of steel; is bold and unshakable
彼かれは心しん臓ぞうが強つよくて、何なにを言いわれても平へい気きだ。
He's got nerves of steel; nothing anyone says bothers him.
〈場ば所しょ〉が心しん臓ぞう部ぶだsomewhere/something is the heart (central, vital part) of a system
この工こう場じょうがわが社しゃの心しん臓ぞう部ぶだ。
This factory is the heart of our company.
心しん臓ぞうに負ふ担たんをかけるto put strain on the heart
過か度どな運うん動どうは心しん臓ぞうに負ふ担たんをかける。
Excessive exercise puts strain on the heart.
〈人ひと〉は心しん臓ぞうが弱よわいsomeone is timid; can't handle stress or shocking things
彼かの女じょは心しん臓ぞうが弱よわいので、怖こわい話はなしは苦にが手てだ。

Expressions

度ど胸きょう sense 2
心臓 (in phrases like 心臓が強い) and 度胸 both convey nerve or boldness, but 度胸 is a standalone noun for courage while 心臓 needs a set phrase to carry that meaning.
中ちゅう心しんN3sense 3
心臓 (as in 心臓部) and 中心 both mean 'center,' but 心臓 stresses vital importance like a literal heart, while 中心 is the neutral word for a geometric or organizational middle point.
核かく心しんN1sense 3
心臓 (metaphorically) and 核心 both mean the vital core of something, but 核心 is used for the essence of an issue or argument, while 心臓 is used for physical systems or organizations.
ハート
心臓 refers to the physical heart organ, while ハート is more often used for the heart shape or the symbolic/emotional heart.
心しんN2
心臓 is the everyday standalone word for the physical heart organ, whereas 心 read しん appears only as a compound element in technical terms like 心拍.

腎じん臓ぞう sense 1
心臓 is the heart, while 腎臓 is the kidney; the two words sound very similar (しんぞう vs じんぞう) and are frequently mixed up by learners.
肝かん臓ぞうN1sense 1
心臓 refers to the heart, whereas 肝臓 refers to the liver; both share the kanji 臓 and are often confused as organ names.
心こころN5sense 1

個こN5sense 1
心臓 is counted with 個, the generic counter used for organs and small discrete objects, as in 人工心臓が一個.

Sino-Japanese word from 心 (heart/mind) and 臓 (internal organ). The figurative senses developed from the organ's central role.

She's a bit timid, so scary stories aren't her thing.

心臓 is the physical heart organ, while 心 refers to the mind or emotional heart; the English word 'heart' covers both, so learners often mix them up.

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心しん筋きん
心臓 refers to the heart as a whole organ, while 心筋 refers specifically to the muscle tissue that makes up the heart wall.
胸むねN3
心臓 is the physical heart organ itself, while 胸 refers to the chest area where its beating is felt, not the organ.

cardiac death

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