Sky,

IMO the word for heart belief is faith. The secondary definition of faith is “belief in God based on spiritual apprehension rather than proof”….Oxford dictionary. An atheist does not believe in God because the proof is lacking and the atheist cannot claim to be spiritually informed…..to do so would be admission that God exists. In our own lives we have witnessed that beliefs are subjective to new knowledge…..faith is not subject to change….pure faith can only grow stronger. One can and does have reason to doubt beliefs but not so with faith. Unfortunately people commonly make faith synonymous with beliefs…….