The purpose of this study is threefold: first, to ascertain whether there are differences between mortality rates associated with coronary artery bypass graft (CABG) surgery in Ontario hospitals that perform such surgeries; second, to test whether the aggregate CABG mortality rate in Ontario is changing; and, third, to test whether the aggregate CABG mortality rate in Ontario is different than the aggregate CABG mortality rate in US states for which comparative data are available.