Slow heartbeat

Traffic jam slowing the delivery truck

Imagine a delivery truck (the heart's electrical signal) that normally leaves the warehouse (SA node) every 1 second and travels through a relay station (AV node) before splitting into two routes to two neighborhood hubs (left and right bundle branches) that distribute packages (blood) to houses (organs). When the traffic jam happens at the relay station or on the highways to the neighborhoods, the truck leaves the warehouse just as often, but it takes forever to reach the hubs — or sometimes gets stuck and never arrives at all. The neighborhoods still need their packages, so delivery piles up at the relay station or the main highways instead of reaching the houses. The body tries to compensate by loading each truck heavier (stronger squeeze) and redirecting what little flow exists toward the most critical neighborhoods (brain and heart), but eventually some houses stop getting power and start running dark. If the jam gets complete, the truck stops moving entirely and the neighborhoods go dark forever unless someone manually reroutes an emergency supply truck.