Pulmonary Embolism (PE) or Extension of RV Thrombus: The patient's history of right ventricular (RV) thrombus increases the risk of pulmonary embolism, which can present with fever among other symptoms like chest pain and dyspnea. An extension of the existing thrombus could also lead to increased inflammation and fever.

Infective Endocarditis: Although less common, infective endocarditis can occur in patients with a history of thrombi, especially if the thrombus is related to or has caused any valvular damage. Fever is a hallmark symptom.
Deep Vein Thrombosis (DVT): Patients with a history of thrombi are at increased risk of developing DVT, which can cause fever due to inflammation.
Sepsis: Any patient presenting with unexplained fever should be considered for sepsis, especially if there's a potential source of infection.

Septic Pulmonary Embolism: This is a rare but potentially deadly condition where the pulmonary embolus becomes infected, leading to sepsis. It's crucial to consider this diagnosis in a patient with a history of RV thrombus and fever.
Intracardiac Shunt Infection: If the patient has any form of intracardiac shunt (either congenital or acquired), there's a risk of shunt infection, which could present with fever.

Marantic Endocarditis: Also known as non-bacterial thrombotic endocarditis, this condition involves the formation of sterile vegetations on heart valves, often in the context of hypercoagulable states or malignancy. It's rare but could be considered in a patient with unexplained fever and a history of thrombi.
Chronic Thromboembolic Pulmonary Hypertension (CTEPH): While not typically presenting with fever as a primary symptom, CTEPH is a complication of recurrent pulmonary emboli and could be a consideration in the differential diagnosis of a patient with a history of RV thrombus and unexplained symptoms.