Paul McCartney wrote this as Hey Jules, a song meant to comfort John Lennon's 5-year-old son Julian as his parents were getting a divorce. The change to Jude was inspired by the character Jud in the musical Oklahoma! (McCartney loves show tunes)
The medical term for a slow heart rate is bradycardia; generally defined as a heart rate below 60 bpm (beats per minute). In contrast, tachycardia means fast heart rate above 100 bpm.
Updated:Mar 23,2016. Bradycardia = too slow. A heart rate of less than 60 beats per minute (BPM) in adults is called bradycardia. What's too slow for you may depend on your age and physical condition. Physically active adults often have a resting heart rate slower than 60 BPM but it doesn't cause problems.