This study sought evidence for linkages between the deceleratory evoked cardiac response (ECR) commonly observed in the OR context and the primary bradycardia of the Laceys. Individual HR protocols from a parametric study of the unitary OR were examined for both cardiac effects. Because of the small amount of data, a procedure of time-series analysis was initially used to remove respiratory sinus arrhythmia noise from the individual protocols. Previous criticism of the uncritical use of this procedure in situations with systematic respiratory changes led to statistical adjustment for this variable by covariance analysis. Evidence was obtained for a brief deceleratory ECR which failed to show the effects of stimulus novelty or intensity that were apparent in the GSR. This slowing of the heart rate began in the cardiac cycle containing the stimulus onset, as expected of primary bradycardia. The magnitude of this immediate slowing showed the dependence upon cardiac phase associated with primary bradycardia, and was also unaffected by stimulus novelty or intensity. These results support a view of the ECR as a cumulative primary bradycardia reflecting stimulus registration, a preliminary process in OR elicitation. © 1983, Psychonomic Society, Inc.. All rights reserved.