(A–B) Twitch force (A) and passive force (B) at 8% elongation of NRVM cardiobundles cultured statically for the entire 14 days (Stat) or treated after first 7 days of static culture with either 20 μM phenylephrine (Stat+PE) or dynamic culture (Stat→Dyn) for the following 7 days. (C) Twitch kinetics, measured by total duration (Total), rise time (Rise), and decay time (Decay) of the twitch. (D–E) Conduction velocity (CV, D) and action potential duration (APD, E) of cardiobundles during 2 Hz point stimulation. (F–G) Fold change in expression of indicated genes (Table S4) relative to static (Stat) group (n = 7–10 cardiobundles per group from 2 cell isolations for each figure panel). *, p < 0.05 vs. Stat, #, p < 0.05 vs. Stat→Dyn.