['Prolongation of QT dispersion can be observed in some patients with myocardial infarction and serves as a possible independent risk factor for sudden cardiac death. Angiotensin-converting enzyme (ACE) inhibition has been shown to reduce QT dispersion in myocardial infarction patients. We hypothesized that ACE gene I/D polymorphism, which is known to modulate ACE activity, may also affect QT dispersion after myocardial infarction.', 'We studied 609 myocardial infarction patients (532 men, aged 56.1+/-0.3; mean 5.5 years after myocardial infarction) from a population-based myocardial infarction register by standardized questionnaire, anthropometry, ECG, echocardiography, and genotyping of ACE I/D polymorphism. In addition, 540 unaffected siblings (251 men, age 54.6+/-0.4 years) of these patients were studied by the same protocol. As compared with their healthy siblings, mean QT dispersion was prolonged in myocardial infarction patients (65.9+/-1.4 ms vs 91.2+/-2.3 ms, respectively, P<0.001). QT dispersion was negatively correlated to left ventricular ejection fraction (P<0.005). The ACE DD-genotype was associated with longer QT dispersion in myocardial infarction patients (103.0+/-4.6 ms vs 81.9+/-4.5 ms in the II group, P<0.001). This association was noted to be strong in multivariate analyses that included age, gender, ejection fraction, left ventricular end-diastolic diameter, medication, and heart rate. In contrast, no association between the ACE DD-genotype and QT dispersion was detected in healthy siblings of myocardial infarction patients.'] Is the D-allele of the ACE polymorphism related to increased QT dispersion in 609 patients after myocardial infarction?