When faced with an electrocardiographic recoding of a complex arrhythmia, we often use inflexible algorithms or try to recall patterns already seen, which is often insufficient to explain the mechanisms of difficult bradycardias and tachycardias. We propose an approach to these situations where, starting from basic observations, the behavior of the different components of the arrhythmia is reconstructed using logical deductions. The extensive use of laddergrams faithfully illustrates how analysis of timing of each visible event, P and QRS, clarifies their relationship and dictates the behavior of electrocardiographic silent cardiac structures (sinus node and atrioventricular node).