Is mild tricuspid regurgitation with epap=29mmhg serious? normal lv good systolic function what could be the cause?

Mild TR by itself is not clinically important but what causes TR is important. Mild increased pulmonary artery pressure causes the mild TR so the etiology of increased PAP is the key. A person with chronic pulmonary disease such as chronic bronchial asthma, COPD, etc. can have mild PAP but we are more concerned with the case of idiopathic or primary pulmonary hypertension which can progress.

Mild tricuspid regurgitation seen on echocardiogram is often a trivial & insignificant finding, However your pulmonary artery pressure is borderline high which can affect the tricuspid valve. I would be guided by what the cardiologist feels about this after examining you and studying the echocardiogram thoroughly.