Die sporthorlosie meet die hartklop.

Because die is the definite article the in Afrikaans.

So the sentence breaks down as:

• Die sporthorlosie = the sports watch
• die hartklop = the heart rate / the heartbeat

Afrikaans uses die for definite nouns, and it does not change for gender the way some other languages do.

No. Afrikaans does not have grammatical gender like German or Dutch.

That means:

• die man = the man
• die vrou = the woman
• die kind = the child

So in your sentence, die is used simply because both nouns are definite.

Afrikaans very often forms compound nouns by writing them as a single word.

So:

• sport = sport
• horlosie = watch / clock
• sporthorlosie = sports watch

This is very common in Afrikaans, just as in Dutch and German. English often writes similar ideas as two words, but Afrikaans usually joins them.

Here, meet means measures.

It looks exactly like the English verb meet, but it is a completely different word in meaning. In Afrikaans:

• meet = measure
• Ek meet my pols. = I measure my pulse.

So in this sentence, Die sporthorlosie meet die hartklop means the watch is measuring heart rate.

Afrikaans verbs do not usually change form depending on the subject in the present tense.

Compare:

• Ek meet = I measure
• Jy meet = you measure
• Hy meet = he measures
• Die sporthorlosie meet = the sports watch measures

So unlike English, Afrikaans keeps the same verb form.

It can refer to heartbeat, and in a sentence like this it is often understood as heart rate.

Literally:

• hart = heart
• klop = beat / knock

So hartklop is the heart’s beating. In the context of a sports watch, English would usually translate it naturally as heart rate.

Yes. This is a basic main-clause word order:

• Die sporthorlosie = subject
• meet = verb
• die hartklop = object

So the pattern is:

Subject + Verb + Object

That is very similar to English in a simple statement: The sports watch measures the heart rate.

A rough English-friendly guide is:

• sporthorlosie ≈ SPAWRT-hor-LO-see
• hartklop ≈ HART-klop

A few helpful notes:

• g is not in these words, so there is no tricky guttural sound here.
• r in Afrikaans is usually rolled or tapped more than in most English accents.
• The o sounds are not always exactly like English oh, but the rough guide above is good enough for a learner.

Yes, in some contexts die can also mean those.

For example:

• die boeke can mean the books
• in the right context, daardie / dié / die-type forms may relate to those

But in your sentence, die is simply the ordinary definite article the. Nothing special is happening here.

If you wanted to say The sports watches measure the heart rate, you would make sporthorlosie plural:

• singular: die sporthorlosie
• plural: die sporthorlosies

So the sentence would be:

Die sporthorlosies meet die hartklop.

Notice that:

• die stays the same
• meet stays the same
• only the noun changes to plural

Not naturally in the same meaning.

If you want to say A sports watch measures heart rate, the more natural Afrikaans would usually be:

’n Sporthorlosie meet die hartklop.

or, depending on context,

’n Sporthorlosie kan hartklop meet.
= A sports watch can measure heart rate.

Using die hartklop makes the object sound definite and normal in this sentence. Dropping die may sound less natural unless the wording is adjusted.