שמתי לב שהוא נשמע עייף, וגם הבחנתי שהוא מדבר לאט יותר היום.

Yes. שמתי לב is a very common fixed expression meaning I noticed or I paid attention.

Literally, שמתי means I put, and לב means heart, so the literal idea is something like I put my heart to it. But in normal Hebrew, you should understand it idiomatically as I noticed.

For example:

• שמתי לב לטעות = I noticed the mistake
• שמתי לב שהוא עייף = I noticed that he was tired / seems tired

Because ש־ means that and introduces a subordinate clause.

So:

• הוא = he
• שהוא = that he

In this sentence:

• שמתי לב שהוא נשמע עייף = I noticed that he sounds tired
• הבחנתי שהוא מדבר לאט יותר היום = I observed that he is speaking more slowly today

English can sometimes omit that, but Hebrew often uses ש־ in this kind of sentence.

Great question. With a noun, those prepositions usually appear:

• שמתי לב לפרט הזה = I noticed this detail
• הבחנתי בשינוי = I noticed a change

But when a whole clause follows, Hebrew very often just uses ש־:

• שמתי לב שהוא נשמע עייף
• הבחנתי שהוא מדבר לאט יותר היום

In more explicit Hebrew, you might sometimes see:

• שמתי לב לכך שהוא...
• הבחנתי בכך שהוא...

But the shorter version in your sentence is completely natural.

Here נשמע means sounds.

So הוא נשמע עייף means he sounds tired.

The verb comes from the root שמע, which is connected to hearing. In this sentence, the idea is that based on how he sounds, he seems tired.

Depending on context, נשמע can sometimes mean things like is heard or sounds, but here the natural meaning is clearly sounds.

Yes.

• נשמע עייף = sounds tired
• נראה עייף = looks tired

So נשמע is based on what you hear, while נראה is based on what you see.

That makes this sentence more specific: the speaker is noticing tiredness from the person’s voice or manner of speaking, not necessarily from appearance.

Because it agrees with הוא, which is masculine singular.

Hebrew adjectives must agree in gender and number with the person or thing they describe.

Here are the main forms:

• עייף = masculine singular
• עייפה = feminine singular
• עייפים = masculine plural
• עייפות = feminine plural

Since the sentence says הוא = he, the correct form is עייף.

Because Hebrew does not backshift tenses the way English often does.

The main verbs:

• שמתי = I noticed
• הבחנתי = I observed

are in the past, because the speaker is reporting what they noticed.

But the clauses after them use present forms:

• הוא נשמע עייף
• הוא מדבר לאט יותר היום

This is natural in Hebrew when describing an ongoing state or action that the speaker observed.

So Hebrew can say, very naturally:

• I noticed that he sounds tired
• I noticed that he is speaking more slowly today

where English might sometimes prefer sounded or was speaking, depending on context.

It can mean either one, depending on context.

Hebrew present tense often covers both:

• he speaks
• he is speaking

So הוא מדבר לאט יותר היום could be understood as:

• he is speaking more slowly today
• he speaks more slowly today

In this sentence, because of היום and the observational context, the progressive sense is speaking is probably the best fit.

They are very close in meaning, but there is a slight nuance.

• שמתי לב is very common and everyday: I noticed
• הבחנתי can sound a little more deliberate, careful, or formal: I observed / I noticed / I detected

So using both in one sentence gives a slightly more natural stylistic variation than repeating the same phrase twice.

Very roughly:

• שמתי לב = everyday noticing
• הבחנתי = noticing with a bit more attention or discernment

Hebrew usually forms comparisons with יותר, which means more.

So:

• לאט = slowly
• יותר = more
• לאט יותר = more slowly

Unlike English, Hebrew usually does not make a special comparative adverb form like slower/slowerly. It simply adds יותר.

The same pattern works in many places:

• מהר יותר = faster / more quickly
• בשקט יותר = more quietly
• ברור יותר = more clearly

Yes. יותר לאט is also natural Hebrew.

Both of these are used:

• לאט יותר
• יותר לאט

The difference is usually not a big meaning difference. In many contexts, they are just stylistic alternatives.

So your sentence could also be said as:

• הבחנתי שהוא מדבר יותר לאט היום

and it would still sound natural.

וגם means and also.

It connects the second observation to the first and makes it clear that the speaker noticed two separate things:

• he sounded tired
• he was speaking more slowly today

If you removed גם and kept only ו־, the sentence would still be grammatical, but וגם makes the additive meaning more explicit.

Because Hebrew word order is fairly flexible, and putting היום at the end is completely natural.

The end position gives a slight focus to today, as if the speaker is highlighting that this slower way of speaking is noticeable specifically today.

Other word orders are also possible, for example:

• הבחנתי שהוא היום מדבר לאט יותר
• הבחנתי שהיום הוא מדבר לאט יותר

But the version in your sentence sounds smooth and natural.