Stretching of intact rat heart triggers the translocation of αB-crystallin to the elastic I-bands of cardiac sarcomeres. Excised adult rat hearts were perfused with PBS for 30 min, either at low pressure to avoid sarcomere stretch (left) or at high pressure to obtain highly extended sarcomeres (right). Left ventricular sections were immunostained for endogenous αB-crystallin (secondary antibody: FITC-conjugated IgG; top) and counterstained for PEVK titin (secondary antibody: Cy3-conjugated IgG; middle). The representative images for each condition are shown. Higher-power images of the region of interest indicated are shown above the main panels. Arrowheads point to the Z-disk localization of αB-crystallin and arrows to I-band localization. Bottom panels show merged images. Bars, 5 µm.