The fourth chakra is the center of all seven chakras with three below and three above - the center where the physical and spiritual meet (Chopra). The Sanskrit word for the Heart Chakra is Anahata, meaning "unstuck" or "unhurt," a spiritual center where no hurt exists.
When this chakra is open, you are flowing with love and compassion. When it is closed, you are full of grief, anger, jealousy and hatred. Thus, it is vital that all humans work to keep a full, open heart.
Deepak Chopra uses the mantra "Om Mani Padme Hum" to invite the practitioner to open her heart:
It is very good to recite the mantra Om mani padme hum, but while you are doing it, you should be thinking on its meaning, for the meaning of the six syllables is great and vast …. The first, OM … symbolizes the practitioner’s impure body, speech, and mind; it also symbolizes the pure exalted body, speech, and mind of a Buddha….
The path is indicated by the next four syllables. MANI, meaning jewel, symbolizes the … altruistic intention to become enlightened, compassionate and loving….
The two syllables, PADME, meaning lotus, symbolize wisdom….
Purity must be achieved by an indivisible unity of method and wisdom, symbolized by the final syllable HUM, which indicates indivisibility….
Thus the six syllables, om mani padme hum, mean that in dependence on the practice of a path which is an indivisible union of method and wisdom, you can transform your impure body, speech, and mind into the pure exalted body, speech, and mind of a Buddha….
— H.H. Tenzin Gyatso, 14th Dalai Lama, "Om Mani Padme Hum"