Bradycardia (brad-e-KAHR-dee-uh) is a slow heart rate. The hearts of adults at rest usually beat between 60 and 100 times a minute. If you have bradycardia, your heart beats fewer than 60 times a minute. Bradycardia can be a serious problem if the heart rate is very slow and the heart can't pump enough oxygen-rich blood to the body. If this happens, you may feel dizzy, very tired or weak, and short of breath. Sometimes bradycardia doesn't cause symptoms or complications. A slow heart rate isn't always a concern. For example, a resting heart rate between 40 and 60 beats a minute is common in some people, particularly healthy young adults and trained athletes. It also is quite common during sleep. If bradycardia is severe, a pacemaker may be needed to help the heart beat at an appropriate rate.