Xin 
and Fei 
are located in the Upper Jiao. Xin regulates Blood, and nourishes Fei ; Fei regulates Qi, maintains respiration for oxygen exchange, and assists Xin in propelling Blood circulation.
Fei generates pectoral Qi, which permeates through Xin and vessels to promote Blood circulation; Xin nourishes and maintains Fei’s functions of respiration and the governing of Qi. “Qi regulates warmth; Blood regulates immersion.” Pectoral Qi flows between the beat of Xin and the respiration of Fei .