Just as a kite suspends on atmospheric wind currents, so the sternum and heart float upward on the internal winds of breath Anatomically the heart is attached to the posterior border of the sternum, so that whenever the sternum moves, the heart follows. Poses that actively stretch the sternum, such as taking the arms behind the back and clasping the fingers together, serve to life and spread the kite sternum.
Accompanied by full diaphragmatic breathing, we can imagine the sternum broadening width-wise like the horizontal axis through a kite, and extending lengthwise, like the vertical axis. In the way that a kite in the sky must be kept aloft at all times, in yoga practice, and particularly in seated mediation, one must sustain the lift of the sternal kite.
During pranayama, when the chest cavity is inflated, the movements of the kite are constantly changing relative to the currents of prana flowing in the chest. We can visualize the kite string of the sternum traveling through the diaphragm, back along the front margin of the spine, and down to the tailbone where the string is tethered. The tailbone serves to anchor and guide the kite to greater buoyancy via the action of mula bandha.
* Pg 177 Yoga of the Subtle Body by Tias Little.