Bradycardia in adults:

In healthy adults, the heart rate is approximately 60bpm at rest. Bradycardia refers to a slowed heart rate, to below 60bpm. However, for symptoms of bradycardia to be experienced, the heart rate normally has to fall below 50bpm. Bradycardia is not necessarily pathological, as trained athletes tend to have lower resting heartrates. Relative bradycardia is when there is a noticeable drop in the baseline heartrate of an individual. In these situations, the bradycardia does not have to be below 60bpm.

Symptoms associated with bradycardia include:
Fatigue.
Dizziness.
Fainting.
Lightheadedness.
Limitations to physical exertion.
Cold peripheries.
Cyanosis.

Fetal bradycardia:

In the fetus, the normal heart rate can range between 110bpm and 150bpm (although some sources differ on the upper range and accept a heart rate of up to 160bpm as a normal baseline).

A prolonged bradycardia is one which lasts for over 3 minutes, with a drop in the baseline rate by 60bpm or falling to below 80bpm. This is a very ominous sign, normally associated with hypoxia, and could indicate one of the following:

Prolonged cord compression.
Cord prolapse.
Rapid descent.
APH.
Uterine rupture.
Rapid descent.
Following epidural/spinal anaesthesia.
Following vaginal examination.

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