In re: the heart and introspection, I'd like to describe a phenomenon I've encountered during structured meditation / self-hypnosis. Please be advised that this may be dangerous. If you experiment with this please be careful.
Normally, your nervous system adjusts subjective perception to attenuate the sensations of your heart beating (also breathing.) With training and practice it is possible to become consciously aware of the physical fact of the hydrodynamic pulsations that are, have been, and will be a constant feature of your human life. The simplest foot-in-the-door thing to do is to feel your pulse (i.e. put your fingers of one hand on the right spot on the wrist of your other hand) as you enter a hypnotic trance.
The specific phenomenon I want to mention is that, as my consciousness became more and more fully aware of the pulse throughout my body I got closer and closer to "touching my heart with my mind" (I don't know how else to describe it.) The heart and circulatory system experienced from within is an incredible potent living energy flow. It was so deep and intense that I never fully merged with it, instead getting "jerked awake" like when you're dreaming and you start to fall and suddenly wake up instead.
If you experiment please be careful, and whatever you do don't force it: who can say if you might not give yourself some sort of cardiac arrest by wiring up the information flows in your nervous system the wrong way?
I think it's worth pointing out in this connection that Gurdjieff described hypnosis as being caused by a change in the usual pressure of blood flow.