После короткого отдыха пульс придёт в норму.

Because после always takes the genitive case in Russian.

• отдых = rest
• после отдыха = after rest / after a rest

So the noun changes from отдых to отдыха. The adjective must agree with the noun, so короткий also changes to короткого.

That gives:

• после короткого отдыха = after a short rest

It changes because it has to match отдыха in:

• case: genitive
• number: singular
• gender: masculine

The dictionary form is короткий.
Here it modifies отдых, which becomes отдыха, so the adjective becomes короткого.

This is standard adjective agreement in Russian.

Пульс is in the nominative singular. It is the subject of the sentence.

So the basic structure is:

• пульс = the pulse / pulse rate
• придёт = will come / will return
• в норму = into the norm / back to normal

So пульс is the thing that will return to normal.

Also, пульс is a masculine noun.

Because Russian has no articles.

English distinguishes:

• a pulse
• the pulse

Russian just says пульс, and the exact meaning depends on context. In a sentence like this, English naturally uses the pulse, but Russian does not need a separate word for that.

Because the sentence describes a result that will happen after the rest.

Придёт is the future tense of the perfective verb прийти.
Here it means something like:

• will come back
• will return
• will get back

Russian often uses verbs of motion metaphorically, and that is what is happening here: the pulse will come back into a normal state.

The perfective aspect is important because it focuses on the completed result: the pulse will end up normal.

Yes, it is somewhat irregular, and learners often notice that.

The infinitive is прийти. Its future forms are built from a different stem:

• я приду
• ты придёшь
• он/она придёт

So you do not say прийдёт.

This is just a pattern you need to learn with идти / прийти / уйти and related verbs. Also notice:

• ё in придёт is stressed
• In normal printed Russian, ё is sometimes written as е, so you may see придет, but it is still pronounced придёт

This is a very important Russian pattern.

• в норму = into the norm, back to normal
• в норме = in the norm, already normal

Russian uses:

• accusative after в when there is movement or change into a state
• prepositional after в when something is already located in that state/place

So here:

• пульс придёт в норму = the pulse will return to normal

But:

• пульс уже в норме = the pulse is already normal

Норма is a feminine noun, so:

• accusative singular: норму
• prepositional singular: норме

Yes, very much so.

Прийти в норму is a common Russian expression meaning:

• to return to normal
• to recover
• to settle back to normal

It can be used not only for pulse, but for many things:

• давление пришло в норму = the blood pressure returned to normal
• температура пришла в норму = the temperature returned to normal
• он пришёл в норму после стресса = he recovered / returned to normal after stress

So in your sentence, the phrase is very natural and idiomatic.

Yes. Russian word order is more flexible than English.

This sentence begins with the time phrase:

• После короткого отдыха = after a short rest

Then comes the main statement:

• пульс придёт в норму

You could also say:

• Пульс придёт в норму после короткого отдыха.

Both are correct. The version with После короткого отдыха first sounds natural if you want to set the time/background right away.

So the difference is mostly one of emphasis and information flow, not basic meaning.

Because in Russian, a simple adverbial phrase at the beginning of a sentence usually does not require a comma.

So this is normal:

• После короткого отдыха пульс придёт в норму.

English often uses a comma after an introductory phrase, but Russian punctuation works differently. A comma might appear only if the writer wants a special pause or intonation, but in a neutral sentence like this, no comma is needed.

Not exactly.

• придёт в норму = will return to normal once, in the future, with focus on the result
• приходит в норму = is returning / comes back to normal, often describing a process, a repeated situation, or a general statement

So in your sentence, придёт is the better choice because it means that after a short rest, the pulse will end up back in a normal state.

For example:

• После короткого отдыха пульс придёт в норму.
  A specific future result.

But:

• После отдыха пульс обычно приходит в норму.
  A habitual or general statement: after rest, the pulse usually returns to normal.