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In this study, the power dissipated into heat during the propagation of a fatigue crack in very high cycle fatigue regime is studied by infra-red pyrometry on a bearing steel. The thermal results show a significant and very local increase in the temperature just before the fracture. In order to better understand the fish eye propagation of the crack which occurs during very high cycle fatigue regime, a thermomechanical model was developed. To describe the evolution of the growth rate law of the crack, a Paris law was used. The fatigue crack is modelled by a circular ring heat source whose radius increases in time. The thermal problem is solved numerically by finite element method. The results show a good correlation with the experiments. The temperature evolution allows to detect experimentally the initiation of the crack propagation. These results show that in very high cycle regime, the propagation stage of the crack constitutes a small part of the lifetime of the specimen.