Background: The identification of proteins involved in left ventricular hypertrophy or dilation is likely to have significant impact on clinical management of patients including discovery of new biomarker or therapeutic targets. Therefore we tried to identify the proteins differently expressed in hypertrophied and dilated left ventricle(LV) using human specimen. Methods: Endomyocardial tissues from interventricular septum were obtained from 4 patients(mean age; 49.8짹18.8, M:F =4:0) having hypertrophied LV and dilated LV, which were proved definitely by echocardiogram. We excluded the patients diagnosed as amyloid heart or reversible dilated cardiomyopathy. Sample preparation was done and the samples were separated by two-dimensional gel electrophoresis (2-DE), digested with trypsin and then analyzed using matrix assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). The proteins were identified by peptide mass fingerprinting searching using the Swiss-Prot and NCBI databases. Results: 1. Among the more than 40 proteins that were differently expressed between hypertrophied and dilated LV, we identified 23 proteins. 2. 7 proteins were increasingly expressed in hypertrophy and 16 proteins in dilated LV. 3. Among these proteins, we discriminated 10 proteins that could be relevant with hypertrophy or dilation of LV (table). Conclusions: Hypertrophied and dilated LV show distinctly different protein expression and this finding might be a clue to uncover the pathogenetic mechanism of progression from hypertrophy to dilation of LV.