Table 2.
Comparison of avian and mammalian hearts.
| Heart Similarities | Heart Differences |
|---|---|
| Hearts have to support resting and aerobic activities | Birds have higher metabolic needs. Resting heart rate faster in avian than humans and mice |
| Four-chambered heart | Chambers are larger, more muscular, and smoother in avian than mammals; heart size relative to body mass is larger in birds |
| Four heart valves. Semilunar valves (pulmonary and aortic valves) are tricuspid in both avian and humans | Right AV valve is a single spiral flap in birds, fibrous tricuspid valve in humans. Left AV is tricuspid in avian, but bicuspid in humans (mitral valve) |
| Coronary system runs through the surface of the heart, in the epicardium, and branches into the myocardium | The proepicardial organ that gives rise to the epicardium is continuous in birds, forming a sheet; but consists of groups of epithelial cells in mice that eventually form a continuous sheet |
| Transport of blood includes pulmonary and systemic circulations, with separation of oxygenated and deoxygenated blood | Right aortic arch develops in avian; left aortic arch in mammals |
| Foramen ovale closes after hatching or birth | Atrial septum formed by the septum primum and dorsal mesenchymal protrusion in birds; in mammals, in addition, there is a septum secundum that also contributes to atrial septation |
| Ductus arteriosi close after hatching or birth | Paired ductus arteriosus in avians (left and right ductus arteriosus); single ductus arteriosus in mammals |
| Cardiomyocytes, the heart muscle cells, proliferate during developmental stages in both avian and mammals increasing the heart size | Shortly after birth, mammal cardiomyocytes binucleate and stop proliferating. Further heart growth is due to volume increase. Avian cardiomyocytes continue to proliferate after hatching, and binucleate at slower rates than mammals. Binucleated avian cardiomyocytes can proliferate. Cardiac growth is due to both proliferation and volume increase |
| Red blood cells are present in both avian and mammals to supply oxygen to organs | Red blood cells are nucleated in avian; not nucleated in mammals, but with a larger time span than in avians |