The concept of defense relates to the idea that organisms react physiologically to the presence of danger or threat in order to protect themselves from potential injury or death. This article reviews the literature on cardiac defense, a specific defense reaction that has a long tradition in psychophysiological research. The review begins with a brief analysis of the two traditional approaches to understand this autonomic response: the cognitive -- linked to Pavlov, Sokolov, and Graham's work on sensory reflexes -- and the motivational -- linked to Cannon and Selye's work on the concepts of activation and stress. Then, the classic model of cardiac defense and its basic assumptions concerning differentiation from other cardiac reflexes -- namely orienting and startle -- are presented. A critical analysis of these assumptions follows centered on evidence from a systematic research of the cardiac response to intense acoustic stimulation. Finally, an integrative model of cardiac defense is presented which emphasizes the dynamic nature of this defense reaction - characterized by a complex pattern of heart rate changes with accelerative and decelerative components, with sympathethic and parasympathetic influences, and with both attentional and motivational significance - providing a new framework in which the two opposite traditional approaches can be reconciled.