Research is mounting that a natural, potent source of stress relief is right in front of your nose. New science is showing that slowing down and deepening your breathing can have profound effects on well-being. Many researchers can't imagine how something so simple could actually have effects on physiology," says Dr. Andrew Weil, a physician and founder of the Arizona Center for Integrative Medicine at the University of Arizona. Breathing exercises - a staple of mindfulness and yoga practices - have been shown to help control blood pressure, improve heart rate, make arteries more flexible and activate the parasympathetic nervous system, which tamps down the body's fight-or-flight response to stress. Weil and other experts now believe deep breathing has a place in a clinical setting. "It's enough to warrant applications in several areas of medicine," says Dr. Luciano Bernardi, an internal-medicine professor whose research shows that slow-breathing exercises improve exercise capacity in patients with chronic heart failure. "We've shown that this simple thing has a fantastic series of effects.