Перегрев опасен для сердца.

In Russian, the verb to be is normally omitted in the present tense.

So:

• Перегрев опасен для сердца. literally looks like Overheating dangerous for the heart
• but it naturally means Overheating is dangerous for the heart

If you were speaking about the past or future, a form of to be would appear:

• Перегрев был опасен для сердца. = Overheating was dangerous for the heart
• Перегрев будет опасен для сердца. = Overheating will be dangerous for the heart

Перегрев is a noun, not a verb. It means overheating or overheating/overheating of the body or something else, depending on context.

It comes from the idea of heating too much:

• греть = to heat
• перегреть = to overheat
• перегрев = overheating

So in this sentence, перегрев is the subject.

Because Russian often uses the short form of adjectives after the subject when saying something is a certain way.

Here:

• опасный = the long form adjective, usually used before a noun
  
  • опасный перегрев = dangerous overheating
• опасен = the short form, used in statements like is dangerous

So:

• Перегрев опасен. = Overheating is dangerous.

This is a very common pattern:

• План важен. = The plan is important.
• Этот метод полезен. = This method is useful.

That ending shows it is the short-form masculine singular adjective.

It agrees with перегрев, which is a masculine singular noun.

Short-form patterns often look like this:

• masculine: опасен
• feminine: опасна
• neuter: опасно
• plural: опасны

Examples:

• Жара опасна. = Heat is dangerous.
• Это опасно. = This is dangerous.
• Такие условия опасны. = Such conditions are dangerous.

Для requires the genitive case.

So:

• dictionary form: сердце = heart
• after для: для сердца = for the heart

This is why сердце changes to сердца.

A few similar examples:

• для ребёнка = for the child
• для организма = for the organism/body
• для здоровья = for health

Here it is genitive singular, not plural.

That can confuse learners, because -а / -я endings are often associated with plural in other contexts, but here:

• nominative singular: сердце
• genitive singular: сердца

So для сердца means for the heart, not for hearts.

Yes. Russian can sometimes use the dative with words like опасен:

• Перегрев опасен сердцу.

This is grammatical, but для сердца sounds more natural and transparent for many learners in this kind of general statement.

Very roughly:

• опасен для сердца = dangerous for the heart
• опасен сердцу = dangerous to the heart

Both are understandable, but для + genitive is extremely common when talking about effects on health.

Перегрев опасен для сердца is a completely normal, neutral word order:

• Перегрев = topic/subject
• опасен = predicate
• для сердца = complement

Russian word order is flexible, though, and changes emphasis more than basic meaning. For example:

• Для сердца перегрев опасен.
  This puts more emphasis on for the heart.
• Опасен для сердца перегрев.
  This is more marked and less neutral.

For a simple textbook-style statement, Перегрев опасен для сердца is the best default order.

The stress is:

• перегрЕв
• опАсен
• для сЕрдца

So the sentence is pronounced approximately:

pyeree-GRYEF a-PA-syen dlya SYERD-tsa

A few pronunciation notes:

• е after a soft consonant often sounds like ye
• для is pronounced as one quick word, roughly dlya
• сердца has the cluster рдц, which can feel awkward at first; listen carefully to native audio if possible

It can refer to both, depending on context.

Russian перегрев can mean:

• overheating of a machine, engine, device, etc.
• overheating of the body
• even figurative overheating, such as an overheated economy in some contexts

So this sentence could easily be used in a medical or health context, especially because of для сердца.

Yes, and it gives a slightly different nuance.

• опасен = dangerous
• вреден = harmful

So:

• Перегрев опасен для сердца. = overheating is dangerous for the heart
• Перегрев вреден для сердца. = overheating is harmful to the heart

Both are natural. Опасен can sound a bit stronger or more serious.

It is neutral standard Russian. It would work well in:

• medical advice
• health articles
• educational materials
• normal conversation

It does not sound especially formal or especially casual. It is a straightforward factual statement.

Sometimes yes, but перегрев is the more natural and common choice here.

Both are related to the idea of overheating, but:

• перегрев is the usual everyday noun
• перегревание can sound more process-focused or technical, and often less idiomatic in a simple sentence like this

So Перегрев опасен для сердца is the better version to learn first.