Atrium (heart) Atrium (heart) The atrium is the upper chamber in which blood enters the heart. There are two atria in the human heart – the left atrium connected to the lungs, and the right atrium connected to the venous circulation. The atria receive blood, and when the heart muscle contracts they pump blood to the ventricles. All animals with a closed circulatory system have at least one atrium/auricle (humans have two atria). The atrium used to be called the "auricle", and that term is still used to describe this chamber in, for example, the "Mollusca", but in humans that name is
Electrical conduction system of the heart has a regular rate of 40 to 60 bpm. These "junctional" rhythms are characterized by a missing or inverted P-Wave. If both the SA node and the AV junction fail to initialize the electrical impulse, the ventricles can fire the electrical impulses themselves at a rate of 20 to 40 bpm and will have a QRS complex of greater than 120 ms. In the event of arrhythmia, a pacemaker may be surgically inserted into the conduction system. Electrical conduction system of the heart The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node to cause