A 45-year-old patient presents with a sudden onset of shortness of breath, chest pain, and a rapid heart rate. The patient has a history of oral contraceptive use and recent long-distance air travel. Which treatment needs to be started immediately to prevent this patient's condition from worsening?

Coumadin, or warfarin, is an oral anticoagulant that is typically used for long-term management of thromboembolism. However, it requires several days to achieve therapeutic anticoagulation and is not suitable for immediate treatment in acute cases. Initiating Coumadin would not address the urgent needs of this patient.

Aspirin is an antiplatelet agent that is commonly used for cardiovascular protection but does not provide sufficient anticoagulation in cases of venous thromboembolism. While it may be beneficial in certain scenarios, it is not the appropriate treatment for immediate intervention in this patient's acute presentation.

Metoprolol is a beta-blocker used primarily for managing hypertension and certain cardiac conditions. While it may help with heart rate control, it does not address the underlying thromboembolic issue. Initiating metoprolol would not treat the acute symptoms or prevent the potential worsening of the patient's condition.