(emphasis added):
"There have been times when I've been 100% certain in my mind and in my heart"
The heart is just a blood pump. Nothing more. But then, it wouldn't sound very emotionally convincing if you fundies said 'Let Jesus into your brain' now, would it?
I know that the human heart is merely a muscle that just circulates blood around the body, taking oxygenated blood from the lungs (when we inhale) to the rest of the body; equally returning deoxygenated (CO2) blood to the lungs for extraction (when we exhale). I'm no medical student, but I know sufficiently about human physiology to acknowledge that fact (thank goodness for my education - biology - which included Darwin's "On the Origin of Species"; religion was taught completely separately, in RE/Comparative Religions. In Britain's state, secular schools. Which encourage thinking for yourself).
But 'God' doesn't, or he'd have stated otherwise - without the need for metaphor or fancy imagery. If indeed, the Bible is the 'Word of God'.
...or simply because there was little to no knowledge of human physiology at the time the Bible was actually written. By men.
Nowadays we know a great deal about the human body. And that the brain is the centre of emotion, personality, learning; what makes us us. 'Cogito ergo sum' indeed.
But God doesn't. Even to this day (otherwise, the Bible would have been rewritten to take into account scientific fact. It'd make for a far more credible read, but would then defeat it's whole purpose, if 'mysteries' were explained).
Therefore proving the superiority of the creation to the creator. Ergo, the answering of the age-old philosophical question: Did God create Man, or did Man create God?.
QED.
"However, the Christian God testifies the heart is deceitful."
Well, you fundies have certainly deceived yourselves into the insane concept of 'spirituality', 'religious belief' and 'faith'. Unconscious honesty, much?
"I have great peace in knowing that."
Well, they say that 'Ignorance is bliss'...!
I'll stick with my scientific facts, thanks. Infinitely superior to 'faith', I find.