Questions & Answers about Er hat Schmerzen in der Brust.
Why is it der Brust and not seiner Brust to mean "his chest"?
In German, you usually use definite articles (der, die, or das) instead of possessive pronouns (like seiner) for body parts when ownership is obvious. Because "he" is the subject of the sentence, we already know whose chest is hurting.
Why does the preposition in trigger the dative case (der Brust) here?
The preposition in is a two-way preposition. It takes the dative case when describing a fixed location, answering the question "where?" (wo?). The pain is located statically in the chest, so the feminine noun die Brust changes to its dative form, der Brust.
We say "chest pain" in English. Why is Schmerzen plural here?
English often uses singular words like "pain" or "ache" for physical ailments, but German strongly prefers the plural Schmerzen for general aches in a specific body part. You will see this same pattern in words like Kopfschmerzen (headache) or Bauchschmerzen (stomachache).
Does die Brust translate to "chest" or "breast"?
It translates to both! Depending on the context, die Brust can refer to the entire chest or thorax area (as it does here with internal pain) or to a breast.