Summary
People who do a lot of sports tend to have a low heart rate, so-called bradycardia. Normally the heart rate (pulse) is between 50 and 80 beats per minute. However, the heart rate can drop to as low as 30 beats per minute at rest, especially for endurance athletes.
In some endurance athletes, electrocardiography (ECG) shows certain cardiac arrhythmias (AV blockages of the first and second degree) due to the slowed heartbeat. The reason for these cardiac arrhythmias is that sport trains the heart and the cardiac conduction pathways to beat efficiently at a lower heart rate under high stress. These bradycardic (slowed) cardiac arrhythmias can lead to various symptoms ranging from a short-lasting circulatory collapse with loss of postural control (vasovagal syncope) to severe dizziness and short-lasting unconsciousness (syncope).
