What the lexicon says. The entry for לֵב (lev, H3820A) gives as its first sense "inner man, mind, will, heart, understanding", and beneath it "mind, knowledge, thinking, reflection, memory", "inclination, resolution, determination (of will)", "conscience", "heart (of moral character)", "as seat of appetites", "as seat of emotions and passions" and "seat of courage" (TBESH, from the abridged Brown-Driver-Briggs). Strong's own 1890 definition says the same thing in a sentence: "The heart; also used (figuratively) very widely for the feelings, the will and even the intellect; likewise for the centre of anything." Thinking is not a stretched sense of this word. It is in the first line of the definition.
What the text does with it. Proverbs uses it for the place decisions are guarded: "Keep thy heart with all diligence; For out of it are the issues of life" (Proverbs 4:23, ASV), the tagged text has H3820A there. And 1 Samuel sets it against appearance: "for man looketh on the outward appearance, but Jehovah looketh on the heart" (1 Samuel 16:7, ASV).
A named reference work makes the same point. The 1915 International Standard Bible Encyclopedia, in its article "Heart" by J. I. Marais, records that "'Heart' in this connection is sometimes rendered 'mind'", and that "'heart' comes to stand for 'conscience,' for which there is no word in Hebrew". It quotes John Owen: "The heart in Scripture is variously used, sometimes for the mind and understanding, sometimes for the will, sometimes for the affections, sometimes for the conscience, sometimes for the whole soul."
⚠️
One caution about the number you may see beside this word. H3820 has two distinct entries: H3820A, the ordinary word for heart, appears in 550 verses; H3820B appears in one, Jeremiah 51:1, where Leb-kamai is a cipher for Babylon, not a heart at all. A tool that reports the base number will show the same total for both.
Sources: Proverbs 4:23; 1 Samuel 16:7; TBESH entry H3820A; Strong's Hebrew Dictionary (1890), entry H3820; Brown-Driver-Briggs (1906), entry H3820; ISBE 1915, "Heart" (J. I. Marais).
---