Fibrosis and myofilament stiffness in AOB. Formaldehyde-fixed (10%) LV tissue samples were paraffin-embedded, sectioned by microtome, and stained with HE Masson’s tri-chrome. A shows representative 10× brightfield images from the Sham and AOB group. A minor increase in collagen deposition is evident in AOB. The results of the more quantitative hydroxyproline collagen assessment displayed in B revealed a small, but nonsignificant, increase in collagen content in AOB (P = 0.161). Single isolated myofibrils were examined over a range of SL and no difference in myofilament passive stiffness was evident in response to AOB. Sham (n = 8 hearts; open bar) and AOB (n = 8 hearts; closed bar).