Figure 2.

The time course of APD₉₀ shortening following a cycle length change from 450 ms to 300 ms in control for a Langendorff-perfused ventricular preparation, showing the two types of exponential fit. Zero on the time axis is the time at which the cycle length was changed. In the main plot, the data was fitted with a mono-exponential (solid line) and, in the inset plot, the same data was fitted with a bi-exponential. The first 50 s of shortening are clearly better fitted with a bi-exponential. Of nine experiments, all could be fit with a mono-exponential, although in five experiments, the first 30–50 s of data were better fit with a bi-exponential.