A 35-year-old man presents with a 6-month history of progressive fatigue, exertional dyspnea, and occasional palpitations. He has become increasingly short of breath with minimal activity and has lost 4 kg over the past 3 months. He denies chest pain, orthopnea, paroxysmal nocturnal dyspnea, lower extremity swelling, fevers, or night sweats.His past medical history is notable only for mild, intermittent asthma during childhood that resolved in his late teens; he has not used asthma medications for over 20 years. He has no history of allergic rhinitis, sinusitis, or atopic dermatitis. He does not smoke, does not use illicit drugs, and drinks alcohol occasionally. He takes no medications.Review of systems is negative for joint pain, skin rashes, numbness, tingling, or weakness.On physical examination, he appears fatigued but is in no acute distress. Temperature is 36.8°C, blood pressure 110/68 mmHg, pulse 92/min, respiratory rate 18/min, and oxygen saturation 98% on room air. Jugular venous pressure is mildly elevated. Cardiac auscultation reveals a regular rhythm with a soft S1 and S2, and a faint S3 gallop; no murmurs are appreciated. Lungs are clear bilaterally. There is no peripheral edema. No skin lesions, purpura, or nodules are present. Neurologic examination is normal.Laboratory studies:White blood cell count: 13,000/µL with absolute eosinophil count 5,500/µL (normal Hemoglobin, platelet count, renal and liver function tests: within normal limitsESR and CRP: mildly elevatedANA, rheumatoid factor, and ANCA: negativeSerum IgE: within normal limitsUrinalysis: unremarkableEchocardiography demonstrates restrictive cardiomyopathy with biatrial enlargement, impaired left ventricular systolic function (ejection fraction 40%), and evidence of endomyocardial fibrosis. No pericardial effusion is present. Chest radiograph shows no pulmonary infiltrates or nodules.What is the most likely diagnosis?