This question is not about the anatomical validity of the claim (I got tired)!
The Shu"A Yo"D 40:1 rules (based probably on the Gm in Hulin 45b and Rashb"a):
"הַלֵּב יֵשׁ לוֹ ג' חֲלָלִים" - there are 3 cavities of the heart (checking for Treyfah).
Are there any scriptural sources for that?
Can this be linked to the assertion that the heart is the dwelling of emotions (see "heart-labeled-the-seat-of-emotion"? If yes, how?