Exercise intolerance in Ebstein's anomaly is usually attributed to desaturation secondary to right-to-left shunting as a result of a small or distorted left ventricle (LV), significant tricuspid valve regurgitation, right ventricular dysfunction, or a combination of these. We observed one boy (age 15 years) and two women (ages 20 and 29 years) with severe Ebstein's anomaly and strikingly abnormal LV myocardium resembling the features described for LV noncompaction. LV size and systolic function were normal in the two women; the boy had a dilated LV with severely diminished ejection fraction. The LV myocardium was found to be unusually coarse and hypertrabeculated, with small intertrabecular recesses and an irregular endocardial surface. The findings in these 3 patients represent the whole spectrum of mild to severe LV noncompaction. Diastolic dysfunction was present in 2 of the 3 patients. Exercise tolerance was diminished in all. There was no mitral or aortic valve disease. The 15-year-old boy underwent heart transplantation 6 months later for biventricular failure. Thus, Ebstein's anomaly does not seem to be a pathology confined to the right ventricle, but may rarely lead to LV noncompacted myocardium. This LV pathology may be an additional explanation for exercise intolerance or signs of left heart failure in patients with Ebstein's anomaly.