Heart beat from 50 to 55 is dangerous?

Not : Necessaarily unless there are symtoms of lightheadedness/ dizziness and your blood pressure is low. See your doctor.

Not generally: Even though that heart rate falls below the "normal" heart rate in adult human beings, a heart rate in that range that is not accompanied by any symptoms (lightheadedness, weakness, unusual fatigue, or unusual shortness of breath) is usually benign. In addition, the more aerobic exercise that is done chronically, the lower the resting heart rate will go. If symptomatic, however, go see an md.

No if asymptomatic: This is noal in highly conditioned people.