On the cover: X-ray diffraction patterns from wild-type (WT; top), protein kinase A (PKA)-treated WT (middle), and cMyBP-C^/ knockout (bottom) mouse myocardium in relaxing solution. The ratio of intensities of the 1,0 and 1,1 equatorial reflections can be used to estimate shifts of cross-bridge mass from the region of the thick filament to the region of the thin filament. Superimposed are traces of force development during a slack-and-restretch maneuver from WT (top) and PKA-treated WT (bottom) myocardium. Rate constants of force redevelopment can be estimated by fitting the curve with a single exponential equation. See related article, page 244.