Matthew 12:35 immediately expands the principle: good and evil treasure produce corresponding speech, directly applying the 'heart overflows into mouth' idea.

Matthew 3:7 has John the Baptist using the exact 'brood of vipers' phrase to denounce the Pharisees.

Matthew 23:33 repeats 'brood of vipers' — Jesus later uses the same accusation against the Pharisees.

Matthew 15:11 states that what comes out of the mouth defiles, not what goes in — reinforcing that speech reveals the heart, as in 12:34.

Matthew 15:18 explicitly says 'what comes out of the mouth proceeds from the heart,' almost word-for-word the same teaching as 12:34.

Matthew 6:21 teaches that the heart follows one's treasure, reinforcing the principle that the heart's content determines outward behavior, as in the mouth speaking.

Psalm 120:2-4 cries out against lying lips and deceitful tongues, paralleling Matthew's theme of evil speech from an evil heart.

1 Samuel 24:13 says 'Wickedness proceeds from the wicked' — the same principle that evil speech reveals an evil heart.

Isaiah 32:6 explicitly says fools speak folly because their hearts are bent on evil, a clear parallel to Matthew 12:34.

James 3:5-8 describes the tongue as 'a restless evil, full of deadly poison' — expanding on how heart's evil manifests in speech.

Psalm 140:3 uses 'venom of vipers' for evil speech, directly echoing Matthew's 'brood of vipers' and the heart-speech connection.

Luke 3:7 records John the Baptist's identical 'brood of vipers' warning to the crowds.

Psalm 64:3 depicts tongues sharpened like swords, directly paralleling the idea that evil words reveal an evil heart.

Luke 6:45 states the same principle: 'the mouth speaks what the heart is full of' — a parallel account of this teaching.

Psalm 52:2-5 portrays the deceitful tongue plotting destruction, reinforcing that evil speech flows from an evil heart.

Romans 3:10-14 quotes Psalm 14 declaring 'their throat is an open grave' — same link between sinful nature and evil speech.

Psalm 10:7 describes a mouth full of curses and lies, echoing the same link between a wicked heart and evil speech.

Proverbs 15:28 contrasts the righteous heart's careful answer with the wicked mouth's evil outflow—directly parallel to Jesus' teaching.

In Mark 7:15, Jesus teaches that defilement comes from within, reinforcing the heart-speech connection.

Mark 7:20 repeats that what comes out of a person defiles, directly echoing the same internal source of evil speech.

Romans 3:13 describes deceitful tongues and viper's poison — directly paralleling the 'brood of vipers' and evil speech.

Ephesians 4:29 commands only helpful talk, applying the principle that speech reflects the heart's condition.

Proverbs 16:23 says the heart teaches the mouth, a direct parallel to 'out of the abundance of the heart the mouth speaks'.

Proverbs 15:26 links the wicked's thoughts (heart) and the pure's words, emphasizing inner state dictates speech.

Proverbs 15:7 contrasts wise lips with a foolish heart, showing that the heart determines speech quality.

Proverbs 10:20 directly links the tongue's value to the heart's worth, reinforcing that speech reflects the heart.

Proverbs 10:11 contrasts the righteous mouth as a fountain of life with the wicked mouth concealing violence — same heart-speech connection.

Proverbs 6:12 directly links a corrupt mouth to a villain's character — the very principle Jesus applies to the Pharisees.

Psalm 119:172 has the tongue singing God's word, reflecting a righteous heart — contrasting with the wicked overflow Jesus condemns.

Psalm 119:13 has the psalmist speaking God's laws from a devoted heart — the positive counterpart to the evil speech here.

Psalm 94:4 shows evildoers pouring out arrogant words — exactly the kind of speech that reveals a corrupt heart.

Psalm 59:7 depicts enemies spewing sharp words — a direct picture of the evil heart overflow Jesus warns about.

Revelation 13:6 shows the beast's mouth spewing blasphemy — a vivid example of evil speech from an evil heart.

Revelation 14:5 presents the opposite: the redeemed have no lie in their mouths, contrasting with the evil speech here.

Isaiah 59:13 describes 'uttering lying words' from a rebellious heart, paralleling Jesus' point that the mouth speaks from the heart's overflow.

John 8:44 says the Pharisees are of their father the devil — reinforcing the evil nature implied by 'brood of vipers'.

Isaiah 6:5 confesses unclean lips as evidence of sin, paralleling Jesus' point that evil speech reveals an evil heart.

1 John 3:10 distinguishes children of God from children of the devil — aligning with the 'brood of vipers' designation.

Psalm 145:7 celebrates God's goodness with joyful singing — a positive example of heart overflow in praise, opposite of evil speech.

Psalm 36:1 describes the wicked's heart lacking fear of God, a source of evil speech and actions — echoing the overflow principle.

Psalm 14:1 reveals the fool's inner denial of God, which leads to corrupt deeds — illustrating how heart condition drives outward actions.

Nehemiah 6:8 recounts false accusations from Sanballat — an example of lying speech emerging from a corrupt heart, parallel to the principle.