It depends on where the baby is positioned as well as the equipment used.

At my first hospital booking appointment (16 weeks roughly) the midwife after much pushing by me used the doppler and found the heartbeat right away. She said it was unlikely that she would find it because babies are very small at this stage but she did.

At my doctor's the following week I asked to hear the heartbeat even though it is his policy NOT to listen for the heartbeat until past 20 weeks so he refused. Then at the 20 week one it took 20 minutes before he located it. It was very stressful for me waiting to hear it but at the same time I could feel the baby moving so I knew she was alive. His doppler is older and less sensitive than the hospitals which is the reason he couldn't find the hb easily and why he doesn't like checking until 20 weeks.

My point is... try not to stress. Different equipment yields different results and depending on the stage you are at in your pregnancy the heartbeat can be very difficult to find because the baby is so small.

How far along are you? I have a measuring thing that says how big a baby is at each point of the pregnancy that was in the bounty bag with quick-eze which is a guide only but it puts it into perspective of the size of bubs.