Birds and mammals have a complete anatomical and functional seperation of oxygenated and deoxygenated blood flow through the heart. in mammalian heart systemic blood enters the right atrium and then passess through a membranous right atrioventricular valve into the right ventricle . Blood is ejected through the pulmonary semilunar valves via the left and right pulmonary arteries for oxygenation in the lung. The cardiac cycle of the mammalian heart consists of an atrial contaction (systole) and then refilling (diastole), coordinated with a ventricular systole and diastole.
