Figure 1.

 Distribution of diagnostic classes across the three eras. Class is defined according to the modified Canadian consensus conference criteria as used by the Bethesda conference report³ (appendix 1). The proportion of patients undergoing surgery who had a condition of moderate complexity (for example, tetralogy of Fallot) increased, whereas simple conditions (for example, secundum atrial septal defects) decreased and complex conditions (for example, transpositions of great vessels) remained unchanged. The difference in distribution of these cases across the three eras is significant (p  =  0.0134), with the differences accounted for by the decrease in simple cases and increase in moderate cases between era 2 and era 3.