Programmed electrical stimulation (PES), angiographic studies, Holter recording, 12-lead ECG and signal averaged ECG (SAECG, n=63) were performed in 109 consecutive patients with a prior Q-wave myocardial infarction (MI). Sixty-five patients (59 por cento) had TMI-class ) or 1 antegrade perfusion without significant collateral filling of the infarct related artery (IRA) (=poor persuion) and forty four (41 por cento) had either good antegrade or collateral perfusion of the IRA. The severity of corony artery disease or ejection fraction did not differ between the patients with poor or good perfusion of IRA. Heart rate variability and presence of late potentials on SAECG were also similar between the groups. but the dispersion of the QT interval was prolonged in the patients with poor perfusion of IRA (86 +/- 35 ms vs. 69 +/- 27 ms, p<0.01). The patients with poor perfusion of IRA had more often a clinical history of VT compared to those with good perfusion (68 por cento vs 9 por cento, p<0.01). Patets with good filling of the IRA after a prior MI have a low risk for VT, suggesting that preserved perfusion of the infarct scar stabilizes the electrophysiologic substrate.