A 36-year-old female patient complains of general weakness, edemas of her face and hands, rapid fatigability during walking, difficult deglutition, cardiac irregularities. These symptoms developed 11 days after holiday at the seaside. Objectively: face erythema, edema of shin muscles. Heart sounds are muffled, BP is 100/70 mm Hg. In blood: ASAT activity is 0,95 millimole/hl, ALAT-1,3 micromole/hl, aldolase - 9,2 IU/l, creatine phosphokinase - 2,5 micromole P/gl. What method of study would be most specific?