Heart failure cells or siderophages are hemosiderin

Hemosiderin

thumb|Hemosiderin image of a kidney viewed under a microscope. The brown areas represent hemosiderinHemosiderin or haemosiderin is an iron-storage complex. It is always found within cells and appears to be a complex of ferritin, denatured ferritin and other material...

-containing macrophages in the alveoli. The main causes are left heart failure and chronic pulmonary edema

Pulmonary edema

Pulmonary edema , or oedema , is fluid accumulation in the air spaces and parenchyma of the lungs. It leads to impaired gas exchange and may cause respiratory failure...

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In left heart failure, the left ventricle

Left ventricle

The left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...

 can not keep pace with the incoming blood from the pulmonary veins. The resulting backup causes increased pressure on the alveolar capillaries, and red blood cells leak out. Alveolar macrophages ingest the red blood cells, and become engorged with brownish hemosiderin.

In pulmonary edema, alveolar septa get thick and fibrous, again increasing pressure on alveolar capillaries and resulting in leakage of red blood cells which undergo phagocytosis by alveolar macrophages.

Heart failure cells may cause brick-red sputum.