We talk a lot about heart space in yoga, or the energy center associated with the heart known as Anahata Chakra. Anahata Chakra is located at the level of the center of the sternum, but straight back at the front of the spine.
Anahata is said to be the space of love, joy, compassion, balance and grace. It helps us to feel open to new experiences and gratitude for wherever we are in our life's journey.
When the energy in Anahata is deficient, we may feel heavy-hearted, it could be difficult to breath deeply, we might have depression, and our chest tends to cave inwards as we feel the weight of the world on our shoulders. When we have excessive heart energy, we may give too much of ourselves away by putting others' needs above our own. We even can be focused on living vicariously through others.
Because chakras are more esoteric, what I like to call the "yoga woo-woo" part of yoga, we should be wary of claims around what the chakras are and what they can do for you. While I don't personally believe your chakra can be "balanced" by an outside force (a crystal, a person, a healing therapy), I do believe wherever your mind and attention goes is where your energy goes. So it stands to reason if you are feeling sad, some heart opening yoga poses and deep breathing would help you to feel better.
To feel better today, try resting in the following pose for 8-16 breaths, and see if you feel a shift to your mindset. It can be done with a rolled up towel instead of a yoga block, and the lift should be directly beneath the shoulder blades so you feel a gentle stretch across the chest. Also, notice the extra block under the head to ease the neck. The arms could be on the floor instead if your shoulders don't like this version.