Patient data: 64-year old man who, prior to this ECG, had been in normal sinus rhythm. Whatever your level of sophistication in rhythm interpretation (i.e., basic, intermediate, or advanced), this ECG has a little bit of something for everybody. Basic interpreters will undoubtedly recognize the dominant disturbance of rhythm. Intermediate interpreters will probably add more descriptors to their interpretation that will better describe the overall pattern. Advanced interpreters will recognize the unique nature of multilevel conduction and ratios. A laddergram will best elucidate the exact mechanism. I'd like to hear from all types of interpreters.