Mid july i had a pericarditis attack. have seen a cardiologist, but am still suffering from sore ribs and swollen lymph nodes under arms. ?

Long time healing: When lymph nodes swell, they take a long time : many month, even up to a year, to become normal again. Pericarditis has no connection to sore ribs. They're two separate issues.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.