The modified Fontan operation (MF) is the preferred palliative procedure for heterotaxy pts (HP) with complex cyanotic heart disease. Early mortality (EM) after MF has been reported to be greater for HP In our recent experience (1987 – 92) EM after MF has improved dramatically. In order to determine if these improved results applied to HP, we reviewed all HP who had a MF atour institution between 1973 – 92 (n = 111). From 1973–92, 111/839 (13%) pts having a MF were HP 154 (6.5%1 polysplenia, 57 (6.8%) asplenia]. HP were significantly older than non-HP at the time of MF (median age = 11 yrs vs 9 yrs; p < 0.05). We compared EM after MF for HP in two time periods: early 11973–86 In = 49)] and recent [1987–92 (n = 62)]. EM decreased significantly in the recent group [9/62 (14.5%)] compared to the early group 121/49 (43%); p < 0.001]. In our early experience, asplenia pts had increased EM compared to polysplenia pts (65% vs 23%) but, recent experience shows that EM is similar for these two subsets of HP [asplenia: 5/34 (15%) vs polysplenia: 4/28 (14%)]. Many factors, including use of an intra-atrial tunnel, have contributed to these improved results. Despite the recent reduction in EM for HP. this group remains at higher risk after MF than pts with tricuspid atresia (EM = 4%) or double inlet left ventricle (EM = 4%). This is most likely due to increased frequency of complicating features present in HP compared to non-HP For example, atrioventricular valve (AW) repair/replacement, a recognized risk factor for EM, was more frequent in HP than non-HP [28/62 (45%) vs 40/277 (14%); P < 0.001]. In HP who did not have AW procedures EM was 9% (3/34) compared to 21% (6/28) in HP who had AVV procedures. The 9% EM rate observed in HP without AW procedures is not significantly different from the 4% EM rate observed in non-HP (p = 0.2). Survival after MF for HP has improved dramatically. Although HP still experience a greater overall operative risk, some subgroups had EM rates which were not significantly different from non-HP.