['To evaluate, with different pacing modes, acute changes in left ventricular systolic function, obtained by continuous cardiac output thermodilution in various subsets of patients undergoing cardiopulmonary bypass surgery. Increments of mean arterial pressure and cardiac output were considered the end point.', 'Fifty cases electively submitted to cardiac surgery were analyzed. Isolated valve surgery 62%, coronary revascularization 30% and 8% mixed disease. Left ventricular ejection fraction was preserved in 50%,36% had moderate depression,(EF 36%-50%) whereas 14% had severe depression (EF\u2009<\u200935%). Left bundle branch block occurred in 18%. Preoperatively 84% were in sinus rhythm and 16% in atrial fibrillation. The different subgroups were analyzed for comparisons. Right atrial-right ventricular and right atrial-left ventricular pacing were employed in sinus rhytm. Biventricular pacing was also used in atrial fibrillation.', 'Right atrium-right ventricular pacing, decreased significantly mean arterial pressure and cardiac output (2.3%) in the overall population and in the subgroups studied. Right atrium-left ventricle, increased mean arterial pressure and cardiac output in 79% of patients and yielded cardiac output increments of 7.5% (0.40\u2009l/m) in the low ejection fraction subgroup and 7.3% (0.43\u2009l/m) in the left bundle branch block subset. In atrial fibrillation patients, left ventricular and biventricular pacing produced a significant increase in cardiac output 8.5% (0.39\u2009l/min) and 11.6% (0.53\u2009l/min) respectively. The dP/dt max increased significantly with both modes (p\u2009=\u20090.021,p\u2009=\u20090.028).'] Does temporary epicardial left ventricular and biventricular pacing improve cardiac output after cardiopulmonary bypass?