If my dates are accurate, somewhere in the middle of week 6. With a 3mHz doppler. I have my first appt. Thursday, and probably first u/s next week. But....It was distinct and typical "swishing" noise and ranged from 119-135. It was faint, but it was there. DH heard it too, and hes the biggest skeptic. I bought the doppler during the 8th week of my last pregnancy, and could hear loud and clear. It has to be in the correct place early on, and maternal body weight is a factor for success in early detection.