A 23-year-old patient complains of edema and pain in the knee and elbow joints, rapid heart rate, and fever of 38°C. According to the patient's medical history, 2 weeks ago he had acute respiratory viral infection. Objectively, edema of knee and elbow joints is observed. Pulse 94/min, transverse cardiac diameter 14 cm. Auscultation detects weakening of the first heart sound and a systolic murmur at the apex. Complete blood count: leukocytes 9.109/L, ESR 18 mm/hour. Urinalysis: protein 0.033 g/L, leukocytes 6-8 in sight. ECG shows sinus tachycardia, PQ interval 0.24 seconds. What is the most likely diagnosis in this case?