45 patients (13 females and 32 males; mean age-37 years) without an organic heart disease underwent the study, on condition that effective transesophageal, ventricular stimulation was achieved. The transesophageal pacemaker SP-5 made by OBR TEMED ZABRZE was used. Ventricular stimulation threshold and a lock of evident retrograde conduction was estimated during ventricular stimulation with a constant cycle length of 500 ms. To assess concealed retrograde atrioventricular conduction, programmed ventricular stimulation of a 50 ms cycle length was applied between late diastole and left ventricular refraction. Concealed retrograde atrioventricular conduction was diagnosed of a sinus impulse reached later ventricles than that during sinus rhythm preceding an examination. There was no evident atrioventricular retrograde conduction in 15 patients (33%). In 9 of them (60%) programmed stimulation revealed concealed retrograde atrioventricular conduction reaching atrioventricular node. Obtained results indicate, that the transesophageal programmed ventricular stimulation enables to examine concealed a-v conduction phenomenon and can be helpful in approximate localization of retrograde atrioventricular block.