Ef ég heyri þig ekki rétt, þá spyr ég aftur.

Because heyri is the 1st person singular present tense form of the verb heyra (to hear).

• að heyra = to hear
• ég heyri = I hear
• þú heyrir = you hear
• hann/hún/það heyrir = he/she/it hears

So in Ef ég heyri ..., the form matches ég (I).

Because þig is the accusative form of þú.

In this sentence, þig is the direct object of heyri:

• ég = I
• þú = you (subject form)
• þig = you (object form)

So:

• Þú heyrir mig = You hear me
• Ég heyri þig = I hear you

A native English speaker often expects just you in both places, but Icelandic changes the pronoun depending on its grammatical role.

Here rétt means correctly, properly, or accurately.

So heyra þig ekki rétt means something like:

• not hear you correctly
• not catch what you said properly
• not hear you clearly enough

Even though rétt is also the word for right/correct, here it functions adverbially.

Because ekki means not, and here it negates the idea of hearing correctly.

So:

• heyri þig rétt = hear you correctly
• heyri þig ekki rétt = do not hear you correctly

In natural English, we might say If I don’t hear you properly or If I don’t catch that correctly. Icelandic expresses that with ekki rétt.

Ef means if. It introduces a conditional clause:

• Ef ég heyri þig ekki rétt = If I do not hear you correctly

That whole part sets up the condition for what happens next.

Þá means then in this sentence.

So the structure is:

• Ef ... , þá ...
• If ... , then ...

It is very common in Icelandic to use þá after an ef-clause, but it is often optional.

You can say:

• Ef ég heyri þig ekki rétt, þá spyr ég aftur.
• Ef ég heyri þig ekki rétt, spyr ég aftur.

Both are grammatical. Using þá just makes the then relationship more explicit.

Because Icelandic usually follows a verb-second pattern in main clauses.

That means the finite verb usually comes in the second position of the main clause.

So in:

• þá spyr ég aftur

the first element is þá, and the finite verb spyr comes next. After that comes the subject ég.

This is a very common Icelandic pattern:

• Nú fer ég = Now I go
• Þá spyr ég = Then I ask

English speakers often expect then I ask, but Icelandic puts the verb earlier.

Because the initial if-clause already counts as the first element, so the main clause still keeps the verb in second position.

So:

• Ef ég heyri þig ekki rétt, þá spyr ég aftur.
• Ef ég heyri þig ekki rétt, spyr ég aftur.

In the second version, the whole clause Ef ég heyri þig ekki rétt takes the first slot, so the main clause begins with the finite verb spyr, and then the subject ég follows.

That word order is normal in Icelandic after a fronted clause.

Because spyrja is the infinitive (to ask), while spyr is the 1st person singular present tense form:

• að spyrja = to ask
• ég spyr = I ask

So:

• þá spyr ég aftur = then I ask again

This verb is a little irregular-looking, so it is very common for learners to wonder about it.

Aftur means again.

So:

• spyr ég aftur = I ask again

It is placed very naturally at the end of the clause here.

Yes, and that is basically what Icelandic is doing too.

Icelandic often uses the present tense in conditionals like this, just as English does:

• Ef ég heyri ... = If I hear ...
• þá spyr ég aftur = then I ask again

This can describe:

• a general habit
• something that happens whenever the condition is true
• even a near-future situation, depending on context

So the present tense here is completely natural.

Because the sentence begins with a subordinate clause:

• Ef ég heyri þig ekki rétt = If I do not hear you correctly

Then the main clause follows:

• þá spyr ég aftur = then I ask again

In Icelandic, it is normal to separate that introductory clause from the main clause with a comma.

Þ is pronounced like the th in thin, not like the th in this.

So:

• þig starts with a thin-type th
• þá also starts with that same sound

This letter is called thorn. It is one of the letters English used to have long ago, but modern English no longer uses it.