A frequência cardíaca está alta depois do aquecimento.

Because frequência cardíaca is a feminine singular noun phrase, and in Portuguese it normally takes the definite article a when you are talking about a specific thing in context.

• a frequência cardíaca = the heart rate
• frequência cardíaca without the article can appear in headings, labels, or very technical styles, but in a normal full sentence, a sounds more natural.

So A frequência cardíaca está alta... is the standard way to say it.

Because cardíaca is an adjective modifying frequência, and it has to agree with the noun in gender and number.

• frequência is feminine singular
• so the adjective must also be feminine singular: cardíaca

Compare:

• frequência cardíaca
• ritmo cardíaco

Here ritmo is masculine, so the adjective becomes cardíaco.

Portuguese uses estar for conditions or states that can change, and ser for more permanent characteristics, definitions, or identity.

In this sentence, high heart rate is being treated as a current condition, especially after warming up, so está is the natural choice.

• A frequência cardíaca está alta. = the heart rate is high right now / in this situation
• A frequência cardíaca é alta. = would sound more like a general characteristic, depending on context

For exercise, body state, temperature, mood, and many physical conditions, estar is usually the right verb.

For the same reason as cardíaca: adjective agreement.

The adjective alta describes frequência, which is feminine singular, so the adjective must also be feminine singular.

• frequência → feminine
• therefore: alta

If the noun were masculine, you would use alto:

• O nível está alto.
• O batimento está alto. (less standard in this exact meaning, but grammatically possible)

Because de + o contracts to do in standard Portuguese.

This is very common:

• de + o = do
• de + a = da
• em + o = no
• em + a = na

So:

• depois de o aquecimento → normally becomes depois do aquecimento

This contraction is not optional in normal Portuguese. Depois do aquecimento is the correct everyday form.

Here, aquecimento means warm-up, especially in an exercise or sports context.

Examples:

• fazer aquecimento = to warm up
• antes do aquecimento = before the warm-up
• depois do aquecimento = after the warm-up

The same word can also mean heating in other contexts:

• aquecimento global = global warming
• sistema de aquecimento = heating system

So the exact meaning depends on context.

Yes. Após o aquecimento is correct and natural.

The difference is mostly style:

• depois do aquecimento = very common, everyday
• após o aquecimento = slightly more formal or technical

In sports, health, and fitness contexts, both are fine.

Yes. Portuguese allows some flexibility here.

These are all natural:

• A frequência cardíaca está alta depois do aquecimento.
• Depois do aquecimento, a frequência cardíaca está alta.
• Após o aquecimento, a frequência cardíaca está alta.

Putting depois do aquecimento at the beginning gives a little more emphasis to the time context: after the warm-up.

Alta is very natural and common. It corresponds to high in English.

Other possible options:

• elevada = elevated, more formal/technical
• aumentada = increased
• muito alta = very high

So you might hear:

• A frequência cardíaca está alta.
• A frequência cardíaca está elevada.

In everyday speech, alta is probably the most straightforward choice.

Yes, but the meaning shifts slightly.

• frequência cardíaca = heart rate
• batimentos cardíacos = heartbeats / heart beats

In many contexts they are close, but frequência cardíaca is more precise for rate. If you are talking about a measured physiological value, frequência cardíaca is usually the better choice.

You could say:

• Os batimentos cardíacos estão acelerados depois do aquecimento.
• A frequência cardíaca está alta depois do aquecimento.

Both are natural, but they are not always identical in tone.

Because Portuguese also commonly describes measured values with alto/alta.

Examples:

• pressão alta = high blood pressure
• temperatura alta = high temperature
• frequência cardíaca alta = high heart rate

So this is a very normal pattern in Portuguese. You do not need a special verb or structure here.

A rough pronunciation guide in Brazilian Portuguese would be:

a fre-KWEN-see-a kar-DYAH-ka es-TA AL-ta de-POYZ do a-keh-see-MEN-too

Main stress points:

• freQUÊNcia
• carDÍaca
• esTÁ
• ALta
• dePOIS
• aqueciMENto

A few pronunciation notes:

• qu in frequência sounds like a kw sound
• depois in Brazilian Portuguese often sounds like de-poys
• final o in aquecimento is often pronounced like oo in unstressed position

You do not need to pronounce every vowel as strongly as in English; Brazilian Portuguese often reduces unstressed vowels.

The accent marks show stress and sometimes vowel quality.

• frequência tells you the stressed syllable is quên
• cardíaca tells you the stress is on dí
• está tells you the stress is on the last syllable tá

These accents are important in writing and can help distinguish words or guide pronunciation. Portuguese spelling uses accent marks much more systematically than English does.