Atrium (heart) of blood occurs. In birds, mammals, and some other reptiles (alligators in particular) the partitioning of both chambers is complete. 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
Electrical conduction system of the heart of 40 to 60bpm. 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 40bpm and will have a QRS complex of greater than 120 ms. This is necessary for the heart to be in good function. An 'arrhythmia' refers to an abnormal rhythm or speed of rhythm of the heartbeat. An abnormal rhythm or speed is defined as one which is not physiological. A resting heart that beats