Winter swimming can be dangerous to people who are not used to swimming in very cold water. After submersion in cold water the cold shock response will occur, causing an uncontrollable gasp for air. This is followed by hyperventilation, a longer period of more rapid breathing. The gasp for air can cause a person to ingest water, which leads to drowning. As blood in the limbs is cooled and returns to the heart, this can cause fibrillation and consequently cardiac arrest. The cold shock response and cardiac arrest are the most common causes of death related to cold water immersion.