Your heart has a complex electrical system that keeps it beating in rhythm. Sinus bradycardia is a type of slow heartbeat. It's when your heart rate is less than 60 beats per minute. At rest, your heart normally beats between 60 to 100 times per minute. Sinus bradycardia can be normal for some people, like well-trained athletes, and doesn't cause problems. But in others, it can cause problems if not enough blood gets pumped to the body.