There is a correlation between inferior vena caval dimension and the right atrial pressure. Inferior vena caval dimensions can be measured from the subcostal view on echocardiography. If the inferior vena caval size is small (less than 1.5 cm) and collapses with inspiration, the estimated right atrial pressure is below 5 mm Hg. When the inferior vena caval size is normal (between 1.5 to 2.5 cm) and the inspiratory decrease in diameter is more than 50 percent, the estimated right atrial pressure is between 5 and 10 mm Hg. With a normal inferior vena caval size, if the inspiratory decrease is less than 50 percent, right atrial pressure is likely to be between 10 and 15 mm Hg. If the inferior vena cava is dilated (more than 2.5 cm in diameter) and the inspiratory decrease in size is less than 50 percent, the right atrial pressure is estimated to be between 15 and 20 mm Hg. When the inferior vena cava is dilated along with dilatation of the hepatic veins and the diameter does not change with inspiration the right atrial pressure is mostly above 20 mm Hg. Inferior vena caval plethora is the term given to lack of significant inspiratory collapse with a dilated inferior vena cava, an important echocardiographic manifestation of right heart congestion.