Aims: Muscle lim protein (MLP) has been suggested to be part of the sarcomeric stress sensor complex. Mice exhibiting a homozygous knock-out of MLP (MLP-/-) develop an HCM between 4 and 8 weeks after birth. We investigated the changes in the myocardial proteome of MLP-/- mice during the development of HCM. Methods: We analyzed left ventricular samples at three different developmental stages (7 days, 4 and 12 weeks after birth) by 2-Dimensional Difference Gel Electrophoresis and identified proteins which showed abundance changes by mass spectrometry (MS/MS). To confirm these results we performed immunofluorescence studies on cryosections and Western blots on MLP-/- and MLP+/+ heart tissue. Results: More than 200 spots showed significant abundance changes. We clearly assigned more than 40 spots to protein IDs by MS/MS. Our results show that the lack of MLP increases the abundance particularly of sarcomere-associated proteins like four-and-a-half lim domain protein 1 (FHL-1), desmin (2.6fold), cypher (2.7fold) and myozenin-2 (calsarcin-1; >2fold), but also chaperones like HSPB1 (2.5fold), HSPB8 (1.6fold) and alpha-B-crystallin (>6fold). FHL-1 showed the highest abundance increase with >10fold in 4 and 12 week old MLP-/- mice. In 7 day old mice very few changes were detectable, but FHL-1 abundance was already increased. Conclusions: Our results suggest an association of MLP with Z-disc and I-band associated proteins. Furthermore, they imply a linkage between MLP and FHL-1 signaling pathways.