Echo findings are within normal limits except for mild to moderate right ventricular enlargement right ventricular systolic pressure 21 mmhg ? ideas?

Accuracy: Echo is not an accurate or reliable test for rv enlargement. If there is a question, you would need an mri. Often, the absence of associated findings (e.g. Severe tricuspid regurgitation, elevated pulmonary artery pressure, intra cardiac shunting, changes of RVH on ekg, abnormal pulmonary vessels on chest xray) are enough to make rve unlikely.

Look at lungs: Do you smoke? Do you have any history of lung disease? Increased resistance in the vessels in the lung will eventually lead to right ventricular hypertrophy. An echo done thru the esophagus might yield better data. Are the heart valves on the right side of the heart normal?