Plantar Fasciitis: Given the patient's complaint of heel pain without a reported injury, plantar fasciitis is a common condition that causes pain under the heel. It's often associated with swelling and can be related to the patient's history of pain in the left foot.

Ankle Sprain: Although the patient did not report an injury, minor sprains can occur without significant trauma, especially in individuals with previous ankle issues or instability.
Tendinitis: Inflammation of the tendons around the ankle, such as Achilles tendinitis, could cause pain and swelling in the ankle area.
Psoriatic Arthritis: The patient has a history of psoriasis, and psoriatic arthritis can cause joint pain and swelling, including in the ankles.

Deep Vein Thrombosis (DVT): Although less common, DVT can cause swelling and pain in the ankle and leg without bruising. Given the patient's history of cardiac arrhythmias and scheduled echocardiogram, there might be an increased risk for thrombotic events.
Infection: Cellulitis or other infections can cause ankle swelling and pain. Although the patient has a history of acute nasopharyngitis, which is unrelated, any infection should be considered, especially if there's a fever or other systemic symptoms.
Cardiac Causes: Given the patient's cardiac history, including arrhythmias and an upcoming echocardiogram, it's essential to consider cardiac causes of peripheral edema, such as heart failure, although these would typically present with more systemic symptoms.

Rheumatoid Arthritis: Although less likely without other joint involvement, rheumatoid arthritis can cause ankle pain and swelling.
Gout or Pseudogout: These conditions can cause sudden, severe joint pain and swelling, often in the big toe but potentially in the ankle.
Osteomyelitis: A bone infection that could cause pain and swelling in the ankle area, though it's rare and usually associated with trauma, surgery, or immunocompromised states.