Tips to finding heartbeat with stethoscope?

C

I’m a vet nurse and have tried to use my stethoscope a few times to find baby’s heartbeat but with no luck! Currently 27 weeks. Baby moving well and everything, just wanting to find it out of interest. Does anyone have any tips or has had any success? I managed to find my older daughters HB when I was pregnant with her but think it was a fluke 😂