A patient in the ER exhibits weight gain and shortness of breath. What is the likely cause of these symptoms?

When a patient presents with weight gain and shortness of breath, one of the most likely causes to consider is fluid retention exceeding fluid output. This condition can lead to pulmonary edema, where excess fluid accumulates in the lungs, causing shortness of breath due to impaired gas exchange. The weight gain is often a direct result of increased fluid volume in the body, which can be attributed to various factors such as heart failure, kidney dysfunction, or excessive sodium intake.

In contrast, while electrolyte deficiencies might contribute to other symptoms, they are less directly associated with the combination of weight gain and shortness of breath in this context. Cardiac arrest is a critical condition that typically presents with a sudden cessation of cardiac activity, not gradual symptoms like weight gain and dyspnea. Respiratory failure is a serious condition but would not specifically explain weight gain; rather, it usually manifests with severe respiratory distress rather than contributing to fluid overload.

Thus, the association of weight gain and shortness of breath points most clearly to fluid retention issues.