Mama, please ask your OB about this sa next check-up mo or kahit mag-call ka na ngayon para peace of mind, hindi kami dapat mag-assume sa baby's heartbeat kasi alam nila exactly kung normal yan o hindi based sa ultrasound. That said, a few of us moms noticed na ang baby's heart rate nag-change din throughout pregnancy, at it can vary depending sa baby's activity, position, at kung kailan siya nag-move during the ultrasound, pero yung interpretation talaga kailangan ng doctor mo kasi sila ang makakasiguro kung okay lang yan o may kailangan i-monitor. Don't worry too much, ha, most of the time these things are normal, pero better safe na i-clarify agad with your OB!