Histological characterization of cardiomyocyte alignment, localization and maturity in tubular engineered heart tissues. (A) Cross-section of a tubular engineered heart tissue stained for alpha-actinin (green) and nuclei (blue) in low magnification. (B) Cross-sectional view of a tubular engineered heart tissue, stained for (from left to right) dystrophin, myosin light chain, ventricular isoform and myosin light chain, atrial isoform. (C) Cross-sectional view of a tubular engineered heart tissue stained for alpha-actinin (green) and nuclei (blue), low magnification. Insets of 3 parts of the tubular wall are shown in high magnification. (D) Longitudinal section of a tubular engineered heart tissue, dystrophin-stained section and alpha-actinin-stained section (higher magnification). (E) Quantification of sarcomere length in tubular engineered heart tissues (n = 3 engineered heart tissues, >50 sarcomeres per engineered heart tissue).