heart

Dictionary of Biblical Words:

This is commonly spoken of as the seat of the affections, but is not generally so used in Scripture. To use it solely with this meaning would lead to serious error. In the Bible it means the man himself, the inner and true person, as distinct from the outward and, it may be, false person. The heart is thus contrasted with the lip. It is the seat of the whole of man’s moral being. “Believing with the heart” does not mean with the affections, neither does it mean with the intellect (or head) only, but it means the man himself believing.

Concise Bible Dictionary:

The heart is often referred to in scripture as the seat of the affections and of the passions, also of wisdom and understanding—hence we read of “the wise in heart,” also the Lord gave to Solomon “a wise and understanding heart.” It is the center of a man’s being. But before the deluge God’s verdict of man was that every imagination of the thoughts of his heart was only evil continually (Gen. 6:5). A similar verdict is found in Genesis 8:21, after Noah came out of the ark. And the Lord said, Out of the heart of man proceed evil thoughts and every form of wickedness (Mark 7:21). The law required man to love God with all his heart. The reception of the gospel must be in the heart, (Rom. 10:9); and God enables a hearer to receive the good news in “an honest and good heart,” upon which there is fruit (Luke 8:15). In new creation there is a “pure heart,” the Christian being led by the Holy Spirit (1 Tim. 1:5; 2 Tim. 2:22; 1 Pet. 1:22).

Strong’s Dictionary of Greek Words:

Number:
2588 (find all occurrences in KJV Bible)
Greek:
καρδία
Transliteration:
kardia
Phonic:
kar-dee’-ah
Meaning:
prolonged from a primary cor, "heart"); the heart, i.e. (figuratively) the thoughts or feelings (mind); also (by analogy) the middle
KJV Usage:
(+ broken-)heart(-ed)