Describe the conducting circuit in the heart

The heart is a muscular pump which pushes blood out to the body. It does this by contracting the muscle fibres which sqeezes the blood out. The heart has 4 chambers. Blood comes into the top two chambers, called the atria. The atria contract which squeezes the blood down to the bottom 2 chambers, called the ventricles. The ventricles then contract which pushes blood out to the body.

Therefore in order to do this the heart must coordinate it's movements so that the atria contract 1st and then the ventricles contract. It does this by sending off electrical signals and the muscle cells only contract when the electrical signal reaches them. 

The electrical signal starts in an area called the Sino-atrial node in the right atrium. This sends signals across the atria causing the atria to contract. The signals then reach the Atrio-ventricular node which is placed between the atria and the ventricles. Here there is a pause which allows the atria time to contract and lets blood get to the ventricles.

From here the signals are carried in branches almost like electrical wires. The electrical signals go from the AV node down the bundle of His. This splits into 2 branches, one to pass signals to the right ventricle called the right bundle branch. And another branch to pass signals to get to the Left ventricle called the left bundle branch. When the electrical signals get to the muscle cells in the ventricles they contract and push the blood out to the body.