Doxorubicin-exposed hearts also contained the highest levels of superoxide (p < 0.001, compared to controls), which correlated negatively with the mtDNA-encoded respiratory chain activities, such as the COX/SDH ratio (r = -0.57, p = 0.02) and the NADH/SDH ratio (r = -0.52, p = 0.04), as well as with the mtDNA content (r = -0.69, p = 0.003), and correlated positively with the frequency of the 'common' deletion (r = 0.76, p < 0.001) and the MDA levels (r = 0.86, p < 0.001).     ///    NADH DH/SDH and COX/SDH ratios were 37% (p < 0.001) and 27% (p < 0.001) of controls.     ///    "They contained elevated levels of malondialdehyde (MDA) (p = 0.006, compared to controls), which correlated inversely with the COX/SDH ratio (r = -0.45, p = 0.02) and the mtDNA-content (r = -0.75, p = 0.002), and correlated positively with the levels of the 'common' deletion (r = 0.80, p < 0.001). "