Chakra 4 - Heart Chakra

Love

Chakra: Anahata, the Heart Center
Color: Green.
Stones: Emerald. Pink and Green stones. Jade, Moss Agate, Malachite. Tourmaline.
Planets: Venus
Relates to: Emotional empowerment. Love, balance and compassion. Respiration.
Element: Air
Mantra: Yam
Meditation: I love.
Inner State: Compassion.
Sense: Touch

The fourth chakra is the Heart chakra and it is located near the middle of the breast bone, just right of your physical heart. It is a rich green sphere, and it enables you to give and accept love and easily express your feminine side. It is where the emotion of love comes from as well as other positive energies such as joy, happiness, integrity, respect, understanding and generosity.  It is the symbol of spiritual security and healing. Its lesson is forgiveness, unconditional love, letting go, trust, and compassion. It also affects universal oneness.

Balanced Chakra
A balanced Heart chakra makes you compassionate and generous, an empathetic humanitarian. You will be considerate towards others, and honor respect, happiness and joy for yourself as well as others. You will love people around you more easily and have good relationships. You will have the ability to wait for the right partner. 

Blocked Chakra
Signs its not functioning properly are repeating dysfunctional relationships, jealousy, frequent emotional outbursts, high or low blood pressure, allergies, and heart problems. You might find it difficult to love yourself, let alone others. You may be cold and unfeeling, perhaps with feelings of guilt and hatred. You might be paranoid and let your emotions rule you, or feel like you are unworthy of love. You might also withhold love to get a desired behavior from people.

Related Organs
The heart chakra rules the heart, circulatory and respiratory systems, diaphragm, ribs, chest, as well as arms, shoulders, hands and thymus gland. It is related to AIDs as well as different types of cancers, particularly breast cancer.

 Activation
When meditating, sit cross legged and let the tips of your index finger touch the thumb. Place your left hand on your left knee, and your right hand over your heart. Focus on your heart.

Sources:
How To Open Chakras - http://howtoopenchakras.com/
Learning About Chakras - http://healing.about.com/cs/chakras/a/learnchakras.htm
Eclectic Energies | Opening the Chakras - http://www.eclecticenergies.com/chakras/open.php
Major Chakras - http://www.wingmakers.co.nz/Chakras.html
The Book of Yoga, by Christina Brown (2002)