APD and CV restitution measured in a thin strip of uniform tissue. Panels (a) and (b) show APD restitution for the steep and flat variants of the model, and in each case the green line indicates the difference in APD produced at each DI. Panels (c) and (d) show the CV restitution for the steep and flat variants of the model. Model variants with restitution shown in red were allocated to region R1, and those shown in blue allocated to region R2. S3 is blocked in R1, because the tissue is still repolarising from the S2 action potential.