mRNA expression profiling Sample preparation, labeling, and array hybridizations were performed according to standard protocols from the UCSF Shared Microarray Core Facilities and Agilent Technologies (http:// www.arrays.ucsf.edu and http://www.agilent.com). Total RNA quality was assessed using a Pico Chip on an Agilent 2100 Bioanalyzer (Agilent Technologies). RNA was amplified using the Sigma whole transcriptome amplification kit following the manufacturer’s protocol (Sigma-Aldrich), and subsequent Cy3- CTP labeling was performed using the NimbleGen one-color labeling kit (Roche-NimbleGen). The size distribution and quantity of the amplified product was assessed using an Agilent 2100 Bioanalyzer and a Nanodrop ND-8000 (Nanodrop Tech- nologies); the labeled DNA was assessed using the Nandrop 8000, and equal amounts of Cy3 labeled target were hybridized to Agilent human whole genome 4644 K Ink-jet arrays. Hybridiza- tions were performed for 14 hrs, according to the manufacturers protocol. Arrays were scanned using an Agilent microarray scanner and raw signal intensities were extracted with Feature Extraction v.10.1 software (Agilent Technologies). Data were further analyzed using Ingenuity Pathways Analysis (IngenuityH Systems) to identify biological pathways involved in CM differentiation. The false discovery rate (FDR) from the data set was used for canonical pathways analysis. Statistics Student’s t-test was used to compare the means of the frequency count distributions of FPdur and FPrise. A value of p,0.05 was considered significant. These analyses were performed using SPSS v.16 (SPSS, Inc.) for Macintosh. The mRNA expression array dataset was normalized using the quantile normalization method [33]. No background subtraction was performed, and the median feature pixel intensity was used as the raw signal before normalization. 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