AV block

Traffic light broken between two cities

Imagine two cities (atria and ventricles) connected by a single highway checkpoint (AV node). Normally, the checkpoint has a traffic light that holds cars for 0.12 to 0.20 seconds—long enough for the first city to empty its warehouses into trucks—then flashes green to let all trucks roll into the second city at once, which then unloads everything. The AV node is like that checkpoint light; it delays signals the way a red light delays traffic. When the AV node breaks (gets damaged, poisoned, or clogged), the light stays red too long (first-degree block: PR interval stretches), flickers and drops random cars (second-degree block: some beats skip), or jams completely (third-degree block: the two cities send traffic on completely separate schedules). Because trucks now arrive at the second city much slower or not at all, the goods (blood) pile up, pressure builds in the warehouses (atria), and the receiving dock (ventricles) sits idle. The backup generator—a slow manual dispatch system in the second city itself (escape rhythm)—tries to keep some trucks moving, but at a crawl.