Fig. 2.

Stimulation frequency is inversely correlated with electrical excitability. A: example strength-duration relationship for the same neonatal rat ventricular myocyte 3-dimensional (3D) spheroid aggregate paced at 1, 2, and 3 Hz. B: ratio of threshold voltage for a constant stimulation duration while pacing at 2 vs. 1 Hz, n = 3–4 spheroids. C: example strength-duration relationship for the same neonatal rat ventricular myocyte monolayer culture paced at 1 and 3 Hz using a voltage source with a bimodal, biphasic square waveform. Inset is replotted on a log-log scale. D: ratio of threshold duration for a constant stimulation strength while pacing at 3 vs. 1 Hz, n = 3 monolayers. Mean and SE are plotted. *P < 0.05. 2D, 2-dimensional.