Deficiency in cellular thiol tripeptide glutathione (L-gamma glutamyl-cysteinyl-glycine) determines the severity of several chronic and inflammatory human diseases that may be relieved by oral treatment with the glutathione precursor N-acetylcysteine (NAC). Here, we showed that the left ventricle (LV) of human failing heart was depleted in total glutathione by 54%. Similarly, 2-month post-myocardial infarction (MI) rats, with established chronic heart failure (CHF), displayed deficiency in LV glutathione. One-month oral NAC treatment normalized LV glutathione, improved LV contractile function and lessened adverse LV remodelling in 3-month post-MI rats. Biochemical studies at two time-points of NAC treatment, 3 days and 1 month, showed that inhibition of the neutral sphingomyelinase (N-SMase), Bcl-2 depletion and caspase-3 activation, were key, early and lasting events associated with glutathione repletion. Attenuation of oxidative stress, downregulation of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and its TNF-R1 receptor were significant after 1-month NAC treatment. These data indicate that, besides glutathione deficiency, N-SMase activation is associated with post-MI CHF progression, and that blockade of N-SMase activation participates to post-infarction failing heart recovery achieved by NAC treatment. NAC treatment in post-MI rats is a way to disrupt the vicious sTNF-alpha/TNF-R1/N-SMase cycle.