Some viral infections (Coxsackie, Influenca, Enteroviruses, Parvovirus, Adenoviruses, CMV...) can cause myocarditis (heart muscle inflammation) that can be manifested with chest pain, heart rhythm irregularity (beside other symptoms), hard breathing... Miocarditis can be also caused by other infections (Chlamydia, Mycoplasma, Borelia, Streptococcus...) and autoimmune disease.
Can you tell me precisely what was the ECG-report?
What were the laboratory results for ALT, AST, LDH, CP-MB, troponin...?
Echo-cardiography and chest X-ray image can be requested for precise diagnosis.