TNF-α has been shown to be involved in cardiac dysfunction during ischemia/reperfusion injury; however, no information regarding the status of TNF-α production in myocardial injury due to intracellular Ca 2+-overload is available in the literature. The intracellular Ca 2+-overload was induced in the isolated rat hearts subjected to 5 min Ca 2+-depletion and 30 min Ca 2+-repletion (Ca 2+-paradox). The Ca 2+-paradox hearts exhibited a dramatic depression in left ventricular developed pressure, a marked elevation in left ventricular end diastolic pressure, and more than a 4-fold increase in TNF-α content. The ratio of cytosolic to homogenate nuclear factor-κB (NFκB) was decreased whereas the ratio of phospho-NFκB to total NFκB was increased in the Ca 2+-paradox hearts. All these changes due to Ca 2+-paradox were significantly attenuated upon treating the hearts with 100 μM pentoxifylline. These results suggest that activation of NFκB and increased production of TNF-α may play an important role in cardiac injury due to intracellular Ca 2+-overload. © 2004 Elsevier Inc. All rights reserved.