Pacing-induced decrease of left ventricular ejection fraction (LVEF) in patients with coronary artery disease has been proposed as a sign of myocardial ischemia, whereas a slight increase or no change is speculated to be the normal response to rapid atrial pacing. The studies of the pacing-induced effects in normals, however, are of limited value, because of either inhomogeneous patient population or different, mainly non-invasive, methods for determination of LVEF. It was therefore the aim of the present study to assess the pacing-induced changes of left ventricular ejection fraction in a homogeneous group of patients. In 10 patients (mean age: 48 +/- 2 years) with normal coronary arteriograms and normal LV-function at rest, rapid atrial pacing was performed stepwise to a maximal pacing rate of 150 beats per minute. In all patients left ventricular end-diastolic pressure LVEDP and time constant of relaxation period tau decreased, while the parameter of contractility Max Dp/dt increased due to increase in heart rate. Furthermore, there was no limited coronary reserve or myocardial lactate production during atrial stimulation as a sign of pacing-induced ischemia. In all patients biplane ventriculography was performed at rest and during maximal stimulation. While end-diastolic volume index EDVI decreased in every patient (71 +/- 5----42 +/- 4 ml/m2, p less than 0.005) and systolic volume index did not change (17 +/- 2----14 +/- 2 ml/m2, N.S.), there was a significant decrease of ejection fraction from 75 +/- 2 to 66 +/- 3% (p less than 0.005). Basal heart rate, age, sex or basal ejection fraction did not influence the response of ejection fraction to rapid atrial pacing. Even after drug-induce afterload reduction there was a significant pacing induced decrease of ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)