To elucidate which clinical features produce U-wave inversion, 339 patients with severe narrowing of the left anterior descending artery were evaluated. In patients with anterior myocardial infarction, extensive coronary artery disease and protected left anterior descending arterial territory are essential in the development of U-wave inversion, whereas electrocardiographic changes at rest in addition to anterior lead ST depression, rather than coronary anatomy, are important in those without anterior myocardial infarction.