The musical discourse may be described in terms of an intricate flow of local groupings. Such groupings, whose perception does not always reach a state of explicit awareness, mostly remain in an informal form, except the most predominant of them, which contribute to more global constructions and will be remembered as the characteristic thematic materials of the musical piece. There have been some attempts, in particular Reti’s thematic analysis, to explicitly describe music at this level of detail. But such non-reductionist approach of music analysis, facing huge complexity, desperately needs automation and objectivity. Current researches in Musical Pattern Discovery, which may be considered as first steps towards this ideal, hardly discover the basic musical structures expected by musicologists. This failure stems from the fact that current formalizations of musical patterns do not take plainly into account the essential characteristics of music as a perceptual phenomenon. We propose a new approach of Musical Pattern Discovery, founded on perceptual heuristics, with the ideal aim of making explicit all the structural details that we more or less implicitly perceive. Basic principles and algorithms are described and illustrated, and first promising results are shown.