Development of Bradycardia during Submersion of the Duck

SOME mammals and birds display structural and functional adaptations which permit them to endure submersion asphyxia for extended periods of time. Among the adjustments to submersion of diving animals, those concerned with the cardiovascular system are the most frequently described. The most conspicuous and easily observable features displayed during submersion are a sudden onset of apnœa followed by a striking bradycardia.