Background: Toll like receptor 4 (TLR-4) is a protein located in the cell membrane with an important function in the immune response of the organism. Its activation decreases heart contractility and activates nuclear transcription factor kappa B (NF-kB ). This in turn, increases the synthesis of different pro-inflammatory cytokines and the inducible enzyme nitric oxide (iNOS), which plays an important role in the inflammatory processes when nitric oxide production is enhanced. Aim: To determine if, after one session of acute exercise, expression of TLR-4 and iNOS, and activation of NF-kB are induced in rat cardiac tissue. Material and Methods: Exercise and control groups of eight male Wistar rats each, were studied. The exercise group was subjected to an acute exercise bout lasting one hour. After the exercise, the heart was excised to measure the expression of iNOS and TLR-4 genes by quantitative polyme-rase chain reaction, NF-kB activation by electrophoretic mobility shift assay (EMSA) and p50 by Western blot. Results: After exercise, there was an increase in TLR-4 and of iNOS mRNA levels (+46.7 and +74.3% respectively). NF-kB activation and the nuclear expression of its p50 subunit also increased significantly (+240 and +306% respectively). Conclusions: Increased expression of TLR4 following a session of acute exercise may contribute to the activation of the NF-kB signaling route, promoting the synthesis of nitric oxide, which could influence negatively the cardiac response to high intensity physical exercise.