The baby's heart starts to beat at around 6 weeks. You may be able to hear – and see – your baby's heart beat for the first time when you're about 8 weeks pregnant if you have an early ultrasound exam. Hearing it for the first time can be very moving. 2  The heart rate of a healthy baby in the womb ranges from about 120 to 160 beats per minute. 3  A heartbeat that's much faster or slower than that may signal a heart problem.