- Humans: 4-chambered heart (2 atria, 2 ventricles)
- Dogfish: 2-chambered heart (1 atrium, 1 ventricle)
2. Blood flow pattern:
- Humans: Double circulation (separate pulmonary and systemic circuits)
- Dogfish: Single circulation (blood passes through the heart once per circuit)
3. Oxygenation of blood:
- Humans: Blood is oxygenated in the lungs
- Dogfish: Blood is oxygenated in the gills
4. Structure of the heart:
- Humans: The heart is divided into four chambers by septa
- Dogfish: The heart has only one atrium and one ventricle and lacks septa
5. Presence of valves:
- Humans: Heart valves ensure proper blood flow and prevent backflow
- Dogfish: Heart valves are absent; instead, muscular sphincters control blood flow