Imbalances in redox status modulate type 3 deiodinase induction in nonthyroidal illness syndrome. However, the underlying mechanisms that lead to D3 dysfunction under redox imbalance are still poorly understood. Here we evaluated D3 induction, redox homeostasis, and their interrelationships in the liver, muscle, and brain in an animal model of NTIS. Male Wistar rats were subjected to left anterior coronary artery occlusion and randomly separated into two groups and treated or not (placebo) with the antioxidant N-acetylcysteine. Sham animals were used as controls. Animals were killed 10 or 28 days post-MI induction and tissues were immediately frozen for biochemical analysis. D3 activity, protein oxidation and antioxidant defenses were measured in liver, muscle, and brain. Compared to those of the sham group, the levels of D3 expression and activity were increased in the liver (P = 0.002), muscle (P = 0.03) and brain (P = 0.01) in the placebo group. All tissues from the placebo animals showed increased carbonyl groups (P < 0.001) and diminished sulfhydryl levels (P < 0.001). Glutathione levels were decreased and glutathione disulfide levels were augmented in all examined tissues. The liver and muscle showed augmented levels of glutathione peroxidase, glutathione reductase and thioredoxin reductase activity (P = 0.001). NAC prevented all the alterations described previously. D3 dysfunction in all tissues correlates with post-MI-induced protein oxidative damage and altered antioxidant defenses. NAC treatment prevents D3 dysfunction, indicating that reversible redox-related remote D3 activation explains, at least in part, the thyroid hormone derangements of NTIS.