The aim of the study was to determine the effect of acute pericardial tamponade on left (LV) and right ventricular (RV) intracavitary and transmural pressure-volume (P-V) relations and to assess the effect of changing blood volume during tamponade on LV and RV volumes. The experiments were done in 11 acutely instrumented anaesthetized dogs in which LV and RV volumes were determined by computed tomography (CT) (n = 5) and LV and RV diameters by sonomicrometry (n = 6). Pressures were measured in the pericardium (balloon transducer), in the aorta and in the ventricles. Incremental pericardial infusion (up to 180 ml) caused a progressive left and upward shift of the LV and the RV intracavitary P-V relationship. This shift was entirely due to increased pericardial pressure (PP). The induction of tamponade caused no change in the LV and RV transmural P-V relationship. During tamponade with ventricular filling pressures above 10-15 mmHg, blood volume expansion caused only minimal increase in LV and RV volumes. In conclusion, pericardial tamponade shifted the LV and the RV intracavitary diastolic P-V relation by increasing PP. However, there was no change in the transmural P-V relationship, indicating unchanged myocardial compliance. Volume loading caused only minimal increase in LV and RV volumes during tamponade.