Relationship between size of the region at risk and size of myocardial infarction. Illustrated are both individual values and regression lines obtained by linear regression analysis for groups I (control group), II (PC group), III (IL-6−/− control group), and IV (IL-6−/− PC group). In groups I, III, and IV, infarct size was positively and linearly related to the risk region size. Linear regression equations were as follows: group I, y = 0.572x + 1.37 (r = 0.83); group III, y = 0.784x − 6.234 (r = 0.92); and group IV, y = 0.910x − 11.42 (r = 0.99). For any risk region size, infarct size was smaller in group II compared with groups I and IV. In contrast, for any risk region size, infarct size was similar in groups IV and III. These data demonstrate that late PC reduced infarct size independent of risk region size and that this effect was abrogated in mice lacking IL-6.