Mér er illt í brjóstinu.

Word for word, it is roughly:

• Mér = to me / for me
• er = is
• illt = bad / painful
• í = in
• brjóstinu = the chest

So the literal idea is something like To me, it is painful in the chest.

That sounds strange in English, but it is a very normal Icelandic way to say My chest hurts or I have pain in my chest.

Because Icelandic often uses the dative case for the person who experiences a physical or mental state.

So instead of saying something like I am hurting with a normal subject in the nominative, Icelandic very often says something more like it is painful to me.

That is why you get:

• mér er kalt = I am cold
• mér er illt = I am in pain / it hurts
• mér er óglatt = I feel nauseous

So mér is the dative form of ég.

Here illt means something like painful, bad, or hurting.

It comes from the adjective illur. In this expression, it is used in a very common Icelandic pattern where a neuter singular adjective describes a general state or condition:

• Mér er illt = I am in pain
• Mér er kalt = I am cold
• Mér er heitt = I am hot

So in this sentence, illt does not mean evil or morally bad. It means physically bad/painful.

That is because illt is not directly agreeing with mér or brjóstinu.

This is an impersonal construction. The adjective is used in the neuter singular as part of a general statement of condition, almost like an unstated it in English:

• Mér er illt = It is painful for me

So:

• it does not agree with mér, because mér is an experiencer in the dative, not the grammatical subject
• it does not agree with brjóstinu, because í brjóstinu is just a location phrase: in the chest

This neuter singular form is very common in Icelandic expressions of sensation.

Brjóstinu is dative singular definite.

That happens because í can take either:

• accusative for movement into
• dative for location in

Here the meaning is location: the pain is in the chest, not moving into it. So Icelandic uses the dative:

• í brjóstinu = in the chest

This is the same basic pattern as:

• í húsinu = in the house
• í bílnum = in the car

Icelandic often uses the definite form of a body part where English would use a possessive like my.

So:

• í brjóstinu literally = in the chest
• but naturally it means in my chest, because the sentence already tells you whose pain it is with mér

This is very common with body parts in many European languages, and Icelandic does it too.

So the sentence does not sound incomplete to an Icelandic speaker.

It can mean either, depending on context.

In a sentence about pain like Mér er illt í brjóstinu, the natural meaning is usually chest.

So a learner should understand:

• brjóst can refer to the chest area generally
• in medical or pain-related contexts, chest is often the best translation

Context decides which English word fits best.

Yes, this is a natural and standard way to express pain.

Icelandic often uses:

• mér er illt ... = it hurts / I am in pain ...
• followed by the body location

So Mér er illt í brjóstinu is perfectly normal.

You may also hear other ways of expressing similar ideas, for example with words meaning pain, ache, or sore, but this sentence itself is idiomatic and good Icelandic.

The main thing to remember is that Icelandic often does not copy the English structure my chest hurts directly.

Normally, no. That sounds unidiomatic.

English often uses have for states and symptoms, but Icelandic often prefers different structures. For pain, the pattern in your sentence is much more natural:

• Mér er illt í brjóstinu

So instead of trying to build it like I have pain in my chest, it is better to learn this as a set pattern:

• mér er illt ...

That will help you sound much more natural in Icelandic.

For a question, Icelandic usually puts the verb first:

• Er þér illt í brjóstinu? = Does your chest hurt? / Do you have pain in your chest?

For a negative, add ekki:

• Mér er ekki illt í brjóstinu. = My chest does not hurt.

So the basic pattern stays the same; you just change the word order for a question or add ekki for negation.