Updated project metadata. In ischemic cardiomyopathy (ICM), left ventricular systolic dysfunction leads to reduced blood flow and oxygen supply to the heart. Alterations in sarcomeric protein function and expression play prominent roles in the onset and progression of cardiomyopathies; however, the molecular mechanisms underlying ICM remain poorly defined. Herein, we have implemented a top-down liquid chromatography (LC)-mass spectrometry (MS)-based proteomics method for the simultaneous quantification of sarcomeric protein expression and modifications in non-failing donor (n = 16) compared to end-stage failing ICM (n = 16) human cardiac tissues. Our top-down proteomics platform provided a “bird’s eye view” of proteoform families with high mass accuracy and reproducibility. In addition, quantification of post-translational modifications (PTMs) and expression reveal significant changes in various sarcomeric proteins extracted from ICM tissues. Changes include altered phosphorylation and expression of cardiac troponin I (cTnI) and enigma homolog 2 (ENH2) as well as a marked increase in muscle LIM protein (MLP) and calsarcin-1 phosphorylation in ICM hearts. Our results imply that the contractile apparatus of the sarcomere is severely dysregulated during ICM. Thus, this study is the first to uncover significant molecular changes to multiple sarcomeric proteins in end-stage ischemic heart failure patients using LC-MS-based top-down proteomics.