In order to assess the reliability of left ventricular ejection fraction as estimated by gated blood pool method, radionuclide angiography (LAO) and single plane (RAO) contrast cineangiocardiography were performed within 14 days in 60 patients with coronary artery disease. The mean value of radionuclide ejection fraction was found to be 55 +/- 16%; contrast cineangiographic ejection fraction was 57 +/- 15%; r = 0.92. In 23 patients with previous anterior myocardial infarction gated blood pool method was found to underestimate left ventricular ejection fraction when compared with contrast cineangiography. The observed underestimation was wide significant in 11 patients with previous anterior infarction, low (less than 50%) radioisotopic ejection fraction and septal akinesia and/or apical dyskinesia; radionuclide ejection fraction = 33 +/- 8%; contrast cineangiographic ejection fraction = 42 +/- 9%; r = 0,76. This study confirms that the values of left ventricular ejection fraction as estimated by gated blood pool method in coronary patients are quite reliable; moreover, the intrinsic variability of the data is low. This may be not true in patients with previous anterior myocardial infarction. The Authors discuss the possible causes of disagreement between radioisotopic and contrastographic ejection fraction in patients with previous anterior infarction and poor left ventricular function: physical problems of measuring ejection fraction by gated blood pool in dilated ventricles; possible mistakes in evaluating blood pool due to the low mobility of the blood mass nearest to the scintillation camera; inhability of contrast cineangiography in RAO to recognize the interventricular septum and evaluate its kinetic abnormalities; unreliability of the geometrical model of revolution elypsoid in calculating end-systolic volumes in ventricles with abnormal wall-kinesis.(ABSTRACT TRUNCATED AT 250 WORDS)