Congestive Heart Failure (CHF): This is the most likely diagnosis given the presentation of symptoms such as shortness of breath, fatigue, and swelling in the legs, which are classic signs of CHF. The condition occurs when the heart is unable to pump enough blood to meet the body's needs, leading to fluid buildup and congestion in the lungs and other parts of the body.

Chronic Obstructive Pulmonary Disease (COPD): COPD can present with similar symptoms to CHF, such as shortness of breath and fatigue, especially in patients with a history of smoking or exposure to lung irritants.
Pulmonary Embolism: A blockage in one of the arteries in the lungs can cause sudden onset of shortness of breath, chest pain, and other symptoms that might be mistaken for CHF.
Anemia: Severe anemia can lead to symptoms like fatigue, shortness of breath, and weakness, which could be confused with CHF, especially if there's an underlying condition affecting the heart's ability to compensate for the lack of red blood cells.
Hypothyroidism: In some cases, hypothyroidism can cause fatigue, swelling, and shortness of breath, mimicking symptoms of CHF, particularly if cardiac involvement is present.

Acute Coronary Syndrome (ACS): Including myocardial infarction (heart attack), ACS is a critical condition that can present with chest pain and shortness of breath, similar to CHF. Missing this diagnosis could be fatal.
Pulmonary Hypertension: Elevated blood pressure in the pulmonary arteries can lead to right heart failure, presenting with symptoms similar to CHF. It's crucial not to miss this diagnosis due to its implications for treatment and prognosis.
Cardiac Tamponade: Fluid accumulation in the sac around the heart can compress the heart and impede its function, leading to symptoms that could be mistaken for CHF. This is a medical emergency.
Aortic Dissection: A tear in the aorta's inner layer can cause severe chest pain and other symptoms that might be confused with CHF, requiring immediate medical attention.

Constrictive Pericarditis: Inflammation of the pericardium (the sac surrounding the heart) can lead to scarring and thickening, restricting heart function and mimicking CHF symptoms.
Restrictive Cardiomyopathy: A condition where the heart muscle becomes stiff, making it difficult for the heart to fill with blood properly, can present with symptoms similar to CHF.
Cardiac Sarcoidosis: Inflammation and scarring in the heart due to sarcoidosis can lead to heart failure symptoms.
Fabry Disease: A genetic disorder that can lead to heart failure among other systemic symptoms, due to the accumulation of a particular type of fat in the body's cells.