У него болит грудь.

Because Russian often expresses physical states like something hurts with a structure that is closer to at him than to he.

So:

• он = he
• у него = literally at him / he has

In sentences about pain, Russian commonly says:

• У меня болит голова. = I have a headache / literally At me, the head hurts
• У него болит грудь. = His chest hurts

So у него marks the person experiencing the pain, not the grammatical subject of the verb.

The basic genitive form of он is его, but after many prepositions, Russian adds н-:

• у него
• к нему
• с ним
• для него

So after у, you must say у него, not у его.

Because in this Russian pattern, the body part is what grammatically hurts.

So the logic is:

• грудь болит = the chest hurts
• у него = for him / in his case

That is why the verb agrees with грудь, not with него.

Because грудь is the grammatical subject of болит.

With болеть in this meaning, the thing that hurts is usually in the nominative:

• болит голова
• болит спина
• болит грудь

If it were accusative, that would suggest it is a direct object, but here it is the thing doing the hurting, grammatically speaking.

Because грудь is singular, and the verb agrees with it.

• грудь болит = singular
• руки болят = plural
• ноги болят = plural

So if one body part hurts, use болит. If several hurt, use болят.

The dictionary form is болеть.

In this sentence:

• болеть = to hurt / to ache
• болит = hurts / aches (3rd person singular, present tense)

So У него болит грудь follows the same pattern as:

• У меня болит зуб.
• У неё болит спина.

Grammatically, you might understand it, but it is not the normal way to say this.

У него болит грудь is the standard, natural Russian pattern for talking about pain.

Его грудь болит sounds more like you are specifically emphasizing his chest as opposed to someone else’s chest, and it is much less neutral.

So for ordinary everyday Russian, use:

• У него болит грудь.

It can mean both, depending on context.

In a sentence like У него болит грудь, it usually means chest.

That is because:

• the subject is male
• the medical or body-area meaning is more natural here

So the sentence is normally understood as His chest hurts.

Yes. Russian word order is flexible, although the most neutral version here is:

• У него болит грудь.

Other orders are possible, for example:

• Грудь у него болит.
• У него грудь болит.

These may add emphasis or sound more conversational depending on context. But for a learner, the safest default is:

• У него болит грудь.

The normal negative form is:

• У него не болит грудь.

That means His chest doesn’t hurt.

You may also hear different word orders for emphasis, but the simplest pattern is:

• У + person + не болит + body part

For example:

• У меня не болит голова.
• У неё не болит спина.

Yes, very common. Russian often uses this exact structure:

• У меня болит голова. = My head hurts.
• У него болит спина. = His back hurts.
• У неё болит рука. = Her arm hurts.
• У нас болят ноги. = Our legs hurt.

So У него болит грудь is not a special exception; it follows a very common model.

Then the verb usually becomes plural:

• У него болят руки. = His hands/arms hurt.
• У неё болят ноги. = Her legs hurt.
• У меня болят зубы. = My teeth hurt.

So:

• one thing hurts → болит
• multiple things hurt → болят

The stress is:

• У негó боли́т грудь.

Approximate pronunciation:

• u nyi-VO ba-LEET groot’

A few notes:

• негó has stress on the last syllable
• боли́т has stress on the second syllable
• грудь ends in a soft consonant

Not in this exact structure.

You normally say:

• У него болит грудь.

There is another possible pattern with a different construction, for example:

• Ему больно в груди.

That means something like He has pain in his chest / It hurts him in the chest.

So both can refer to chest pain, but they are different grammatical patterns:

• У него болит грудь = body part as subject
• Ему больно в груди = painful state felt by him

No. Болеть can also mean to be ill or even to support/root for a team in other contexts.

But in a sentence like this, with a body part in the nominative, it clearly means to hurt / to ache:

• болит грудь
• болит горло
• болит живот

So here the meaning is specifically physical pain.