Schematic of how calculations of dF/dt, −dF/dt, TTP, and RT50 were made in the analysis of twitch data. Data shown were recorded from canine right ventricular trabecula, plotting F_dev (normalized to cross-sectional area assuming ellipsoid shape of muscle, in millinewtons per square millimeter) versus time (in milliseconds). Example tangent lines used to calculate dF/dt and −dF/dt are shown. The length of time from the initiation of the twitch contraction to the maximal F_dev is the TTP. The length of time from the peak F_dev to 50% of the peak F_dev is the RT50.