A 25-year-old woman complains of shortness of breath during physical exertion, fever of 37.8°C, dull pain in the area of her heart, and palpitations. According to the patient's medical history, 2 weeks ago she had a case of an acute respiratory viral infection. Objectively, the skin is pale, pulse 95/min, blood pressure 100/60 mm Hg. Auscultation detects vesicular respiration, respiratory rate 22/min. The heart sounds are rhythmic, the first heart sound is weakened at the apex, a systolic murmur can be heard. ECG shows reduced voltage and negative T wave. Laboratory tests detect elevated levels of AST, LDH, and CPK. What is the most likely diagnosis in this case?