sinzou ha daizi desu.

It is read:

しんぞう は だいじ です

In rōmaji:

shinzō wa daiji desu

A few pronunciation notes:

• 心臓 = しんぞう / shinzō
• The ぞう has a long o sound.
• The particle は is written ha but pronounced wa here.

In normal Japanese writing, it would usually be written without spaces:

心臓は大事です。

When は is used as a particle, it is pronounced wa.

So in this sentence:

• 心臓 = heart
• は = topic particle, pronounced wa
• 大事です = is important / is precious

This is a very common beginner point in Japanese. The spelling stays は, but the pronunciation changes to わ only when it functions as this particle.

は marks the topic of the sentence.

So 心臓は大事です literally feels like:

• As for the heart, it is important.

In natural English, we usually just say:

• The heart is important.

The topic is what the sentence is talking about. Japanese often organizes sentences around a topic rather than around a subject in exactly the same way English does.

Because 大事 is not a verb. It is a word meaning important, valuable, or precious.

In Japanese, you do not always need a verb like to be in the same way English does. With words like 大事, Japanese uses です to make the sentence polite:

• 大事です = is important / is precious

So the sentence is built like this:

• 心臓 = heart
• は = topic marker
• 大事です = is important

大事 is usually taught as a na-adjective.

That means:

• before a noun, it takes な
• at the end of a sentence, it does not use な

Examples:

• 大事な本 = an important book
• この本は大事です = This book is important.

So in 心臓は大事です, 大事 is being used at the end of the sentence, so な does not appear.

Because な is only used when a na-adjective directly modifies a noun.

For example:

• 大事なもの = an important thing
• 大事な人 = an important person

But when the adjective is at the end of the sentence, you do not use な:

• 心臓は大事です = correct
• 心臓は大事なです = incorrect

So the rule is:

• 大事 + noun → 大事な noun
• sentence-final 大事 → 大事です or 大事だ

です makes the sentence polite.

Compare:

• 心臓は大事です。 = polite
• 心臓は大事だ。 = plain / less polite
• 心臓は大事。 = casual, often used in conversation

So です does not really change the core meaning very much here. It mainly affects the level of politeness.

Yes, but the nuance changes.

• 心臓は大事です。 = As for the heart, it is important.
• 心臓が大事です。 = The heart is what is important / It’s the heart that is important.

Using は makes heart the topic.

Using が often gives more focus or emphasis to heart as the thing being identified.

For a simple general statement like this, は is the more neutral choice.

Yes, 心臓 usually means the physical organ, the heart inside the body.

That is different from words like:

• 心（こころ） = heart, mind, feelings, spirit
• ハート = heart, often used in a more symbolic or borrowed-English way

So 心臓は大事です sounds like a statement about the actual bodily organ.

Japanese does not normally use articles like the or a/an.

So 心臓 can mean:

• the heart
• a heart
• hearts in a general sense

The exact meaning depends on context.

In this sentence, English naturally translates it as:

• The heart is important.

But Japanese itself does not explicitly mark the here.

The spaces are only for learning purposes.

Normal Japanese writing would be:

心臓は大事です。

Japanese is usually written without spaces between words. Textbooks and beginner materials sometimes insert spaces to help learners see the parts of the sentence more clearly.

They are very similar, and in many cases either one works.

• 大事 = important, precious, valuable
• 大切 = important, precious, cherished

So you could also say:

• 心臓は大切です。

Both are natural. Very roughly:

• 大事 can sound a little broader and very common in everyday speech
• 大切 can sometimes sound slightly more careful or emotionally valued

But the difference is often small, especially for beginners.