AV Node
It is responsible for conducting electrical impulses from the top 2 chambers of the heart, the right and left atria, to the bottom 2 chambers of the heart, the right and left ventricles.
First Degree AV Block
First-degree AV block refers to a condition where the transmission of impulses through the AV node is slower than expected.
Second Degree AV Block
Second degree AV block refers to a condition where the transmission of impulses through the AV node is slower than expected with occasional times where impulses are not transmitted at all.
Third Degree AV Block
Complete heart block (complete AV block, or third-degree AV block) refers to a condition where the transmission of impulses through the AV node is completely interrupted. In other words, no impulses are able to get through whatsoever.