Idiopathic paroxysmal complete atrioventricular (AV) block is a rare form of a complete AV block. It is characterized by the sudden appearance of the complete AV block from - at that moment - normal AV conduction. It occurs in a structurally healthy heart. The appearance is followed by long asystole and syncope, rarely by sudden cardiac death. Although mentioned in previous years, the entity was first defined in detail by Brignole in 1997, and then other authors. Specific features of this block, which clearly distinguish it electrocardiographically and clinically from other types of AV block are: 1) normal baseline electrocardiogram without AV and intraventricular conduction disturbances; 2) appearance of complete AV block from a normal electrocardiogram, without prior variation of the P-P interval, without slowing or accelerating the sinus frequency, and without the extension of the PQ interval. Not triggered by atrial or ventricular premature beat; 3) absence of lower escape rhythm with shorter or longer asystole 4) Instant AV conduction recovery, without lower degrees of AV, 5) normal conduction system on electrophysiological testing; 6) in anamnesis recurring more or less frequent syncope without prodromal symptoms. Although it is a serious disorder, it is rarely diagnosed due to insufficient knowledge of the entity and its unpredictability. Even when considered, it is difficult to “catch” it without long-term monitoring. Recently, as a cause of this block, low basal adenosine serum levels are reported, leading to A2 receptor hyperaffinity of the AV node with the consequent strong reactivity of the conduction system with a sudden rise in adenosine levels. (1-3) Cardiac pacing is the only reliable method of treatment. In the presentation we will present cases of idiopathic paroxysmal AV block from clinical practice.