--123 atrial pacings (AP) performed as diagnostic investigations in patients with chest pains were re-examined. By using floating catheter without fluoroscopic control, this technique is very simple to perform and free from relevant risks. The diagnostic sensibility and specificity of AP were examined in 93 patients in which a coronary arteriography was performed; these figures were compared with the corresponding values observed in 65 patients in which an adequate diagnostic exercise test (ET) was also available. The diagnostic sensibility of AP examined in 63 patients with significant coronary artery disease was 90%; the corresponding value of ET was 79%. In particular, in patients with single vessel disease, the sensibility of AP (90%) was much higher than that observed in ET (40%). The specificity of AP examined in 30 patients free from significant stenosis of the coronary arterial tree was 43%. This value was largely lower than that observed in ET (82%) in the same patients, and appears to be inadequate for validation AP as a diagnostic tool in coronary heart disease. Therefore, AP must be limited to functional, and not diagnostic, evaluation of patients in which the diagnosis of coronary heart disease can be made by other means.