Yoga, heart and MIND. Awesome article:  Yoga: Changing The Brain's Stressful Habits

"It may sound like magic that posing like a proud warrior or a crow could have such extensive effects, but it's not magic.  It's neurobiology.  This next statement may sound to you either profound or extremely obvious, but it comes down to this: the things you do and the thoughts you have change the firing patterns and chemical composition of your brain.  Even actions as simple as changing your posture, relaxing the muscles on your face, or slowing your breathing rate, can affect the activity in your brain (beyond, of course, the required activity to make the action).  These changes are often transient, but can be long-lasting, particularly if they entail changing a habit."