I rented a doppler a couple of weeks ago and have found the hb 2-3 times since then with no problem. I have had 4 ultrasounds, including one LESS THAN A WEEK AGO and everything was fine. So why, why, why am I stressing because I have tried to find the hb 4 times in the past 3 days and haven't found it any of those times??! I am seriously considering sending the thing back. Any of you doppler users having a similar experience? Or any words of reassurance anyone can give me? Bleh!! I am walking a fine line here of not wanting to use it TOO much, and panicking.