Findings and pathophysiology of right sided congestive heart failure
The cranial vena cava is responsible for draining the unoxygenated blood from the head, thorax and forelimbs into the right atrium. Meanwhile, the caudal vena cava drains unoxygenated blood from the abdomen and the hindlimbs into the right atrium. Therefore, when pressures increase in the right side of the heart, specifically the right atrium, the cranial and caudal vena cava experience an increase in hydrostatic pressure. This increase in hydrostatic pressure in the cranial vena cava or the caudal vena cava causes fluid flux out of the vessels and into the pleural cavity or abdominal cavity respectively.
During the evaluation of thoracic radiographs, fluid in the pleural cavity can be detected by observing certain radiographic features such as: fissure lines and the leafing of lung lobes.