If you google heart definition this is the first response you get:
a hollow muscular organ that pumps the blood through the circulatory system by rhythmic contraction and dilation. In vertebrates there may be up to four chambers (as in humans), with two atria and two ventricles.
the region of the chest above the heart.“holding hand on heart for the Pledge of Allegiance”
the heart regarded as the center of a person’s thoughts and emotions, especially love or compassion.“hardening his heart, he ignored her entreaties”
one’s mood or feeling.“they had a change of heart”
courage or enthusiasm.“they may lose heart as the work mounts up”
the central or innermost part of something.
Here is a Meditation to Open Your Heart by Deepak Chopra.