Exacerbation of Congestive Heart Failure (CHF): The patient's history of CHF, current symptoms of bilateral lower extremity swelling, and recent evaluation by cardiology suggest that an exacerbation of CHF is the most likely diagnosis. The use of Lasix (furosemide) at home and the need for more aggressive treatment in the ER further support this diagnosis.

Nephrotic Syndrome: This condition, characterized by heavy proteinuria, hypoalbuminemia, and edema, could explain the patient's lower extremity swelling. However, it would be less likely given the patient's known history of CHF.
Chronic Venous Insufficiency: This condition could cause bilateral lower extremity swelling, especially in an elderly patient. However, the acute presentation and the patient's recent cardiology evaluation suggest that CHF exacerbation is more likely.
Hepatic Cirrhosis: Liver disease can cause fluid retention and lower extremity edema. While possible, this diagnosis would be less likely without other signs of liver dysfunction or a history suggestive of cirrhosis.

Deep Vein Thrombosis (DVT): Although less likely than an exacerbation of CHF, DVT is a critical diagnosis to consider due to its potential for severe complications, including pulmonary embolism. The patient's age and immobility increase the risk for DVT.
Cellulitis or Infection: Infection of the skin and soft tissues could cause swelling and redness in the lower extremities. Given the patient's age and potential for compromised immune function, it's crucial to consider and rule out infection.
Lymphedema: While less common, lymphedema could cause unilateral or bilateral lower extremity swelling. It's essential to consider this diagnosis, especially if the swelling does not respond to typical treatments for CHF.

Lipedema: A rare condition characterized by the abnormal growth of fat cells in the lower extremities, leading to swelling. It is less likely and typically presents with specific characteristics distinguishable from edema due to CHF.
Sarcoidosis: This autoimmune disease can cause swelling in various parts of the body, including the lower extremities, due to granulomatous inflammation. However, it would be an uncommon cause of bilateral lower extremity swelling in this context.
Superior Vena Cava Syndrome: Obstruction of the superior vena cava can cause edema in the upper body but could potentially lead to lower extremity swelling if there's significant impact on cardiac function or if the obstruction affects venous return from the lower body indirectly. This would be a rare and less likely diagnosis.