This paper reports an investigation which examined the sympathetic and/or parasympathetic mediation of the heart rate response to intense auditory stimulation - the cardiac defense response (CDR) - by recording cardiac period (CP) and pulse transit time (PTT) simultaneously. Thirteen subjects underwent a physiological reaction test with a single presentation of a distorted 400-Hz sound of 109 dB, instantaneous rise time and 0.5 s duration. The results regarding the form of the CDR replicated the typical pattern with four components: two accelerative and two decelerative in alternating sequence. As regards CP and PTT changes the only coincidences occurred in the second accelerative and second decelerative components of the response. In the first two components the changes in CP and PTT moved in opposite directions. These results support a description and interpretation of the CDR in terms of both accelerative and decelerative components with both vagal and sympathetic mediation.