Summary of ventricular and embryonic MHC expression patterns for fetal (E10) and adult myogenic cultures, based on previously published results (Hartley et al., 1991). This summary is limited to the expression of these two isoforms and does not address possible heterogeneity in expression of other MHC isoforms by fibers within fetal and adult cultures as was shown by Stockdale and co-workers (Stockdale and Miller, 1987; Miller and Stockdale, 1989; Feldman and Stockdale, 1991). V+E+, coexpression of ventricular and embryonic MHC isoforms as detected by isoform specific mAbs. V+, expression of ventricular MHC only.