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In this work, the high cycle fatigue behavior of cast hypo-eutectic Al-Si alloys is investigated. It is observed that two different coexisting fatigue initiation mechanisms can occur in these materials depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Si particles, Fe-rich inter-metallics, DAS of the Al-matrix, etc).Firstly, an experimental study is presented, highlighting the coexistence of these two fatigue damage mechanisms and their dependence on the presence of different micro-structural heterogeneities. A probabilistic high cycle fatigue model, which has the capacity to describe these two mechanisms, is then presented. The model contains the same principal ingredients as the one developed by [1]. It uses a probabilistic framework to link the two different fatigue damage mechanisms, and can take into account the mean stress and the effect of a biaxial stress state.INTRODUCTION