A comprehensive thermomechanical investigation has been conducted to study the local kinematic and calorimetric responses of wet glass-fiber reinforced polyamide 6.6 subjected to tensile-tensile low-cycle fatigue tests. Digital image correlation (DIC) and quantitative infrared thermography (QIRT) were combined simultaneously to monitor the onset and development of spatial heterogeneities. Fields of strain, strain rates, intrinsic dissipation and resulting thermoelastic sources were successively observed and thoroughly analyzed with regards to the main fiber orientation and water content. Areas of precocious heterogeneities were detected from the very beginning of the loading, roughly propagating along the main fiber orientation. A ratcheting effect induced by the positive mean stress was observed and accompanied by a slight cyclic creep of the specimens. At high water content, the thermoelastic inversion phenomenon appeared and progressively spread along the gage part of the specimen, highlighting both glassy and rubbery behavior of the samples investigated.