what is the only electrical connection between the atria and the ventricles?
Then the impulse collects, or pauses, in the atrioventricular (A-V) node, located within muscle near the center of the heart, and travels down the ventricles. The A-V node is the only normal electrical connection between the atria and the ventricles. At 3 to 4 millimeters, the sinus and A-V nodes are tiny, the size of a few grains of sugar. Heart block occurs when there is a delay in the conduction of the electrical impulse through the heart. In most cases, heart block is caused by a problem with the A-V node. Complete heart block: The most common type of heart block in children is complete heart block, also called third-degree heart block. In complete heart block, the electrical impulse never gets past the A-V node. The only reason a person can survive is that another, weaker natural pacemaker takes over in the ventricles.