The inventors have developed tools for quantifying the mitochondrial redox state of in vivo, in situ tissue using resonance Raman spectroscopy. The tissue is illuminated with an excitation beam that causes the tissue to scatter Raman-shifted light, which is collected and analyzed to produce coefficients representing the relative concentrations of different chromophores in the tissue. These relative concentrations indicate the redox state of whole mitochondria, hemoglobin oxygen saturation, myoglobin oxygen saturation, and/or redox state of individual cytochrome complexes in mitochondria of the in vivo, in situ tissue. Quantifiable information about these states and/or saturations can be used to assess tissue health, including organ (dys)function before, during, and after surgery. For example, this information can be used to predict impending cardiac failure, to guide surgical interventions, to monitor organ health after transplantation, or to guide post-operative care.