Post-rest potentiation. (A) Traces showing reduced maximal post-rest force in a typical R4496C ventricular trabecula compared with WT. (B) Average percent increase of twitch force after different intervals of stimulation pauses from a basal frequency of 1 Hz in atrial (left) and ventricular (right) R4496C versus WT trabeculae. In atrial trabeculae, absolute maximal post-rest twitch force at a 60-s rest interval was 53.3 ± 9.6 mN/mm² in WT versus 19.9 ± 4.6 mN/mm² in R4496C (P < 0.01). In ventricular trabeculae, maximal post-rest twitch force at a 60-s rest interval was 76.3 ± 15.6 mN/mm² in WT versus 44.3 ± 8.6 mN/mm² in R4496C (P < 0.01). Error bars represent mean ± SEM.