In my experience the Septuagint (LXX) can often serve as somewhat of a "mini-commentary" on the Hebrew passage that it translates.One has to use discretion as the Septuagint translation of some passages are strikingly different from the corresponding Hebrew.In short, we need to guard our heart, because our spiritual heart is the starting point for every spiritual aspect of our life.Don't be deceived by sin (See The Deceitfulness of Sin), for all of us, even the most godly among us, has some residual, innate propensity toward moral failure, some weak point, some potential opening for sin to pierce our moral armor. Continually your soul diligently (exceedingly, very greatly), lest you forget the things which your eyes have seen, and lest they depart from your heart all the days of your life; but make them known to your sons and your grandsons.
Wheaton, IL: Victor Books) Theme: We must be diligent to keep our hearts; because the condition of our heart will affect everything else in our life…
And yet, hardly anyone gives a single thought to "keeping the heart".
(Keep Your Heart, Proverbs Sermon Greg Allen - Bethany Bible Church) . In medical terms, it's when the heart ceases to beat.
Pase (all without exception) phulake (noun: as an action = guarding, watch; a person who stayed on watch at a guard post like our modern sentinel, cp "guard" in Acts 12.10 - see related verb that is the root of phulake = phulasso) (tereo = speaks of guarding something in one’s possession, watching as one would something precious, continually observing attentively.
The present imperative is a command calling for us to make this our habitual practice cp "guarding" in Acts 12:6) sen (possessive adjective = your) kardian (see word study on kardia = heart, see also discussion of heart on this page) gar (for) ek (out of, from) touton (this) exodoi (see word study on exodos--a departure, here in plural = outgoings) zoes (see word study on zoe -- absolute fullness of life, both essential and ethical). The heart is the “master-control” of the life; a wrong heart always produces a wrong life.