i guess they are just hoping it goes away by itself
but inflammation always has a cause - i would push for more
viral pericarditis does often resolve by itself
if its lyme - there are studies showing that blood tests are typically more likely to be positive for antibodies for lyme when the heart is involved ( vs general chronic lyme cases ) - i guess the body is evolved to make a more significant immune response to infections in the heart
so that is one option
lyme can cause pericarditis and myocarditis - and heart block etc - and medical systems do tend to take lyme carditis seriously if diagnosed - as it is a recognised life threatening condition
https://www.ncbi.nlm.nih.gov/pmc/articles/pmc4395762/