SOB and Edema. Doppler appear normal?

I'm a 29-year-old female experiencing intermittent pitting edema in my feet. A comprehensive set of tests was conducted to rule out serious underlying conditions, including liver and kidney function tests (LFT, KFT), complete blood count (CBC), serum glucose, lipid profile, urine routine and protein-creatinine ratio, serum cortisol, and thyroid profile. All results came back normal. Due to the persistent nature of the edema, a 2D echocardiogram was also performed, which was completely normal. The edema was ultimately attributed to prolonged standing. However, l've recently started experiencing shortness of breath while walking, which has made me question whether a 2D echo alone is sufficient to rule out heart failure. Is it possible to have heart failure even if both the echocardiogram and color Doppler appear normal?