The fourth chakra (Heart Chakra) is at the center of the seven chakras with three below and three above. This is the area where physical and spiritual meet. The fourth chakra, also referred to as the heart chakra, is located at the center of the chest and includes the heart, cardiac plexus, thymus gland, lungs, and breasts. It also rules the lymphatic system. When your heart chakra is open, you are flowing with love and compassion, you are quick to forgive, and you accept others and yourself. A closed heart chakra can give way to grief, anger, jealousy, fear of betrayal, and hatred toward yourself and others. (source)
Some crystals that we carry that my help you balance your heart chakra are Rose Quartz, Amazonite, Aventurine, and Lepidolite.