The experiment was to test differential gene expression in early- and advanced-stage heart failure (HF), as well as in normal, HF, and transgenically "rescued" transgenic mice (please reference Blaxall, et al, Physiological Genomics 2003 for further information). Each sample is from a single mouse left ventricle. RNA was isolated using the guanidinium isothiocyanate method, and labeled and hybridized to Affymetrix Mu11K arrays as recommended by the manufacturer.