Objectives. This study was designed to establish whether left ventricular pseudohypertrophy in cardiac tanponade can be reproducibly induced in an experimental canine model and to investigate the mechanism or its production. Background. Past experimental and clinical studies have shown reduction of ventricular volumes resulting from cardiac tamponade. Left ventricular pseudohypertrophy, a transient thickening of myocardial walls, was recently described as a new echocardiographic sign of cardiac tamponade. Methods. Cardiac tamponade was induced in seven anesthetized open chest dogs with serial bolus injections of 50 ml each of 0.9% saline solution into the pericardial sac. Under hemodynamic monitoring, M-mode and two-dimensional echocardiographic measurements were performed from a right parasternal window at each stage of graded cardiac tamponade. Results. There was a progressive increase of interventricular septal and posterior wall diastolic thickness. Mean wall thickness (interventricular septal thickness + posterior wall thickness ÷ 2) was 9.8 ± 1.3 mm at baseline, 14.9 ± 0.9 mm at peak tamponade and 9.0 ± 1.5 mm after fluid withdrawal (p < 0.0001). Mean wall thickness correlated directly with the severity of cardiac tamponade, as estimated from the level of right atrial pressures (r = 0.75 and p < 0.0001), and with the decrease of left ventricular cavity volume (r = - 0.67 and p < 0.0001). Left ventricular mass did not change significantly. Conclusions. Left ventricular pseudohypertrophy is a constant manifestation of cardiac tamponade in a canine model. The degree of myocardial thkkening correlates with the reduction of ventricular dimensions and with the severity of hemodynamk compromise, representing a constant facet of heart remodeling in cardiac tamponade.