An acute blood pressure elevation may cause ventricular ectopic rhythms, while its reduction may alleviate them. It is studied whether the blood pressure exerts some effect on parameters obtained by the signal averaged electrocardiogram. In 25 patients with either hypertension (8 cases) or ventricular ectopic rhythms (10 cases) or both (7 cases) the blood pressure was reduced by sodium nitroprusside (24 cases) and/or elevated with metaraminol (10 cases) and the signal averaging electrocardiogram was recorded under 2 or 3 pressure values on each patient. During the high pressure (193.6 +/- 20.1 mm Hg) the following differences were noted compared to the low pressure (77.4 +/- 15.2 less): longer QRS duration in all 25 patients (+9.92 +/- 10.51 ms, P < 0.001); longer low (< 40 microV) amplitude signals (LAS) in 18 patients (+6.94 +/- 10.93 ms, P < 0.005); lower root mean square voltage of the terminal 40 ms of the QRS in 22 patients (-15.73 +/- 21.60 microV, P < 0.005); and ventricular ectopic beat incidence higher in 8, lower in 1, and equal in 2 cases (with no arrhythmia in the other 14). The generally and focally reduced conduction, as suggested by the QRS and LAS prolongation, might contribute to the proarrhythmic effect of acute blood pressure elevation.