A 37-year-old woman complains of shortness of breath and constricting retrosternal pain. One week ago she had a flu. She has acrocyanosis, her heart rate is 98/min., blood pressure – 90/75 mm Hg, respiratory rate – 26/min. The cardiac borders are expanded to the left and right by 3 cm. The heart sounds are muffled, above the cardiac apex there are a protodiastolic gallop rhythm and a systolic murmur. Hb – 100 g/L, ESR – 25 mm/hour. Make the right diagnosis: