Congestive Heart Failure (CHF): This condition is highly likely given the combination of symptoms such as swollen ankles (edema), shortness of breath (SOB), and frequent urination. CHF leads to fluid buildup in the body, causing these symptoms.

Chronic Kidney Disease (CKD): CKD can cause fluid retention, leading to edema and shortness of breath. Frequent urination could be a sign of the kidneys' reduced ability to concentrate urine.
Nephrotic Syndrome: Characterized by significant proteinuria, hypoalbuminemia, and edema. While less common, it could explain the edema and potentially the shortness of breath if there's associated fluid overload.
Diuretic Resistance or Non-adherence in a Patient with Known Heart Failure: If the patient is already diagnosed with heart failure and is on diuretics, resistance or non-adherence to medication could lead to worsening symptoms.

Pulmonary Embolism (PE): Although less likely given the constellation of symptoms, PE is a life-threatening condition that can cause sudden onset of shortness of breath and could be associated with leg swelling if there's a deep vein thrombosis (DVT) present.
Cardiac Tamponade: A life-threatening condition where fluid accumulates in the sac around the heart, leading to impaired heart function. It can cause shortness of breath and potentially edema if there's significant impairment of cardiac output.
Sepsis: Particularly in elderly patients, sepsis can present with non-specific symptoms including shortness of breath, edema, and changes in urinary output. It's crucial to consider sepsis due to its high mortality rate if untreated.

Constrictive Pericarditis: A condition where the pericardium becomes scarred and contracts around the heart, impeding its function. It can cause edema, shortness of breath, and potentially increased urinary frequency due to fluid overload.
Lymphatic Obstruction: Conditions affecting the lymphatic system, such as lymphoma or filariasis, can cause significant edema. However, these would be less common and might not fully explain the shortness of breath and frequent urination without other symptoms.
Superior Vena Cava Syndrome: Obstruction of the superior vena cava can cause edema and shortness of breath but is relatively rare and usually associated with other specific symptoms like facial swelling.