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Acute Respiratory Distress Syndrome (ARDS) is characterized primarily by severe hypoxemia and the presence of bilateral infiltrates on imaging, such as chest X-rays or CT scans, accompanied by the absence of heart failure as the direct cause of the pulmonary symptoms.

In ARDS, the severe hypoxemia results from impaired gas exchange due to increased permeability of the alveolar-capillary membrane, leading to pulmonary edema and reduced functional residual capacity. The bilateral infiltrates observed on imaging symbolize the non-cardiogenic pulmonary edema seen in ARDS and reflect the diffuse pulmonary inflammation and injury.

It is crucial that the hypoxemia and infiltrates occur in the presence of normal cardiac function, distinguishing ARDS from pulmonary edema due to congestive heart failure. This definition aligns with the Berlin definition of ARDS, which classifies the condition specifically based on these characteristics, emphasizing the need for exclusion of heart failure as a contributing factor.

The other options contain elements that do not accurately describe the defining features of ARDS, either by including incorrect symptoms or characteristics not pertinent to the acute presentation of this syndrome.