BACKGROUND In isolated working guinea pig heart preparations using the conventional technique of cannulating the left atrium via the atrial appendage, the resulting cardiac output is often insufficiently low (15-20 ml/min). This is a problem in ischemia reperfusion studies where small absolute differences can be responsible for large relative changes comparing pre- and postischemic values. In an attempt to increase cardiac output, the left atrium was left intact in isolated working guinea pig hearts. The two techniques were compared for hemodynamic parameters and their similarity to the physiological condition. METHODS The left atrium was cannulated either via the orifices of the pulmonary veins or via an incision in the atrial appendage with its subsequent ligation around the cannula (n = 45-46/group). After 20 min of pressure-volume work cardiac output, heart rate and oxygen partial pressures were measured and myocardial oxygen consumption and cardiac efficiency were calculated. RESULTS Cardiac output was higher in hearts with intact atrial appendage (64 +/- 2 ml/min) than in hearts with ligated atrial appendage (33 +/- 1 ml/min). Myocardial oxygen consumption (6.1 +/- 0.2 and 8.4 +/- 0.3 micromol/min, resp.) and cardiac efficiency (12.8 +/- 0.6% and 19.9 +/- 0.8%, resp.) were significantly higher in hearts with intact left atrial appendage. CONCLUSIONS Isolated working guinea pig hearts with an intact left auricle exhibit higher values for important hemodynamic parameters compared to a preparation technique involving ligation of the left auricle.