In left heart failure (especially left ventricular failure), the heart’s left ventricle becomes weak and can’t pump blood forward properly.
So what happens?
Blood starts backing up into the left atrium.From there, it backs up into the pulmonary veins and pulmonary capillaries.This increases the hydrostatic pressure inside those tiny vessels of the lungs.
When hydrostatic pressure gets too high:
Fluid is forced out of the pulmonary capillaries.It leaks into the interstitial space and eventually into the alveoli (where gas exchange happens).This fluid in the lungs = pulmonary edema → causing breathlessness, especially when lying down (orthopnea).
