After myocardial infarction (MI) viable myocardium between normal and necrotic areas may represent a possible substrate for an abnormal signal averaged ECG (SAE). Myocardial viability can be assessed by low-dose dobutamine (Dob)-Echo on the basis of the contractile recovery of a basal asynergy. Aim of this study was to assess whether Dob-induced improvement in contractility may change SAE in patients (pts) with MI. Twenty-five pts, 19 males, mean age 58 years, underwent a Dob-Echo test 13 +/- 5 days after AMI. SAE (40 Hz, Butterworth filter) was recorded before and during a 6' Dob infusion (10 μg/Kg). Quantitative wall motion analysis of LV divided in 24 segments was done on digitized images and % area changes (%AC) from peak diastolic to peak systolic area calculated by centerline method. Asynergy was found in 111 segments (basal %AC < 30%); segments were considered viable when %AC increased by =< 35% from baseline. Dob improved LV contractility in 13 pts (%AC from 26 +/- 5 to 41 +/- 4) [G I]; In 12 pts [G II] no changes in %AC were observed (from 24 +/- 4 to 24 +/- 6%). Site of MI, thrombolysis, basal EF, peak heart rate at 10 μg/Kg Dob were comparable in both groups; a baseline (B) significantly (p < 0.01) longer fQRS and LAS40 and shorter RMS40 were recorded in G I pts. Shortening of fQRS and prolongation of RMS40 were seen in pts with Dob-induced contractile improvement; in pts with no myocardial viability these parameters had an opposite behaviour.Dob-induced contractile recovery of asynergic areas parallels an improvement in SAE parameters which is likely due to a ''homogenizing effect'' on the myocardium with reduction in delay and fragmentation of ECG activation fronts.