The aim of this study was to investigate if provoked myocardial ischemia induces increased beat-to-beat QRS amplitude variability in patients with angiographically verified coronary artery disease. 15 patients (median age 62 years, range 46-73 years) and 10 healthy controls (median age 25 years, range 22-42 years) were studied. Dobutamine was infused intravenously at a low and at a high dose. The mean low dose of the drug was 10.0 µg/kg/min for both patients and controls, whereas the mean maximum dose was 31 ± 2 for patients and 38 ± 1 µg/kg/min for controls. The total QRS amplitude beat-to-beat variance from 12 leads as well as individual variance scores in each single lead were evaluated. Before infusion, the total QRS variance did not differ between patients and controls, nor did the individual variance in 9 of the 12 ECG leads. Dobutamine elicited an increase (p < 0.01) in the total QRS variance, with significantly higher (p < 0.001) total variance in patients than in controls. At the high dose of the drug, the patients displayed significantly higher individual variance values in each ECG lead as well. During dobutamine infusion, 7 of 15 patients developed ST depressions ( ≧ 0.1 mV in ≧ 2 leads) in 12-lead ECG readings. Eleven of 15 patients developed chest pain (grade > 3 at the Borg’s CR-10 scale). In conclusion, in patients with ischemic heart disease, dobutamine-provoked stress gives rise to increased QRS amplitude beat-to-beat variability, as a sign of electrical instability of the myocardium.