I had a HB seen at 6w2d but that was with a different to normal probe (not internal, just stronger resolution). Was told that with most pgcies, can't see much untill after 8wks unless an internal is done and even then the lower limit is around 6wks. I have pics of my bubs at 6w2d and all you can really see is the gest sac, feotal pole, egg sac and a blur above it which was bubs. A little flicker in the blurr was the HB. 4wks is definitely too early to see anything really. Sorry honey