Significance The present study demonstrates the utility of global phosphoproteomic profiling of diseased cardiac tissue to identify signaling pathways and other biological processes disrupted in cardiomyopathy. Perturbed Notch-1 signaling was identified by bioinformatics analyses of phosphoprotein patterns present in affected cardiac tissue in a transgenic mouse model system of dilated cardiomyopathy and by complementary molecular biology and microscopy techniques. In addition, dozens of other disturbed signaling pathways offer an opportunity for novel therapeutic and/or diagnostic clinically applicable targets. Although this study was performed in mice, only minor adjustments to the experimental approach would be required for comparative analysis of analogous samples from human cardiac patients, potentially leading to even more clinically relevant data.