Can a slow heartbeat be dangerous?

A slow heartbeat may be nothing serious. But it may be a sign of disease, or it may be the side effect of a medication that can cause a slow heartbeat. A “slow” heartbeat is usually defined as below 60 beats per minute at rest (some experts say below 50). Some people have a slow heartbeat but no symptoms. Symptoms from a slow heartbeat include lightheadedness or feeling faint or actually fainting. They also include breathlessness. A person with symptoms that could be caused by a slow heartbeat should be medically evaluated.