Acute pulmonary edema is mostly caused by heart disease such as acute left heart failure, which results in a weakening of the heart’s contraction and a sharp decrease in the heart’s blood output, resulting in poor pulmonary venous return and pulmonary stasis. As the local venous pressure increases significantly in pulmonary stasis, the fluid in the pulmonary capillaries infiltrates into the alveoli and interstitial space, and the exudate contains red blood cells, which makes the exudate appear pink and foamy, resulting in coughing up pink foamy sputum. In addition, because of the edema of the walls of the pulmonary capillaries due to pulmonary stasis, violent coughing can easily cause the capillaries to rupture and bleed, and thus pink foamy sputum can be coughed up. Coughing up large amounts of pink foamy sputum is a characteristic manifestation of acute pulmonary edema, which indicates that the disease is critical and requires immediate resuscitation treatment to avoid life-threatening occurrences.