At my A/S at week 19, they found an echogenic foci on the heart too. The doctor said "everything else looks perfect, but the spot on the heart is a soft marker for downs". But she also said that it has nothing to do with a heart defect and in 90% of cases it goes away on it's own. It does not affect the heart.
Then the genetic counselor asked if I wanted an Amnio or the MaterniT21 test (which I am not doing because now, my stress about it has dissipated). But, the doctor said with my new odds for downs (1/700) it was not a cause for concern, especially because all other tests had been negative.
I immediately freaked of course! I spent a solid week researching everything I could find, and the research helped ALOT! A solitary echogenic foci is really not a "soft marker" for downs, unless it is combined with another soft marker. With the technology now, these foci are found in about 10% of ultrasounds. My doctors office saw it about once a day. I'm not sure why your doc recommended the testing. Mine said nothing further was needed since it was "normal" and didn't affect heart function.