The Xin 
and Shen 
relationship is demonstrated by the interdependence between Fire and water, or Yin and Yang. The energy of Xin and of Shen are constantly interchanged, just as heavenly Qi descends and earthly Qi ascends. Xin fire descends to warm Shen -Yin; Shen -Water ascends to Xin to nurture Xin -Yang and Xin -Yin, and to prevent Xin -Fire from becoming inflamed. “Disharmony between Xin and Shen ” 
may bring on illness.
Deficient Shen Essence and deficient Xin -Blood may similarly cause each other. The disorder of both will finally appear as palpitations, tinnitus, and weakness of the waist and knees.
The Basic Questions says, “The Xin … is the residence of the Mind”; “The Shen stores vital Essence which nurtures the Willpower” . Both quotes indicate the relationship which these viscera have with activities of the human Spirit.