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Figure 4 Action potential duration (APD₉₀) and left ventricular peak (+)dP/dt in single test pulse (restitution) experiments. Sotalol produced a substantial increase in the plateau phase of the electrical restitution curve. The APD with sotalol (at coupling intervals exceeding 400 ms) was significantly higher than that seen in the baseline state and with esmolol (p < 0.001; p < 0.001 for interaction). During the plateau phase of the mechanical restitution curve, left ventricular (+)dP/dt with sotalol exceeded that seen with esmolol at coupling intervals exceeding 600 ms (p < 0.01).