A client with deep vein thrombosis (DVT) in the left leg is on a heparin protocol. Which intervention is most important for the nurse to include in this client's plan of care?

Encourage mobilization to prevent pulmonary embolism.

Measure each calf's girth to evaluate edema in the affected leg.

Observe for bleeding side effects related to heparin therapy.

Assess blood pressure and heart rate at least every 4 hours.