My 4yo had a chest xray, a doc reviewed it said "she has what heart defect? "-uhm, none. Even tho shallow breath view, should I follow up? Yessleepapnea

Well... Although, some heart defects may reveal themselves on the xray, i would get an official radiologist's read on that first. If it appears to be suspicious for a heart defect, then i would go ahead and work it up further with echocardiogram or referral to a heart specialist. The accepted guidelines say - referral to cardiologist.
WHEN IN DOUBT. Reading x-rays can be very subjective, and one would need additonal history to get the right readings. When in doubt, get a second opinion or refer to a pediatric cardiologist to sort things out.