The ability to reliably estimate pulmonary artery wedge pressure measurements using the clinical and basic cardiovascular parameters was assessed in fifty-six patients having elective coronary artery bypass surgery. The patients were divided into three groups: Group 1 had normal left ventricular function (22 patients), Group 2 had moderate left ventricular dysfunction (20 patients) and Group 3 had more severe left ventricular dysfunction (14 patients). The percentages of correct pulmonary artery wedge pressure estimations were 55%, 56% and 52% in Groups 1, 2 and 3 respectively. We conclude that pulmonary artery wedge pressure measurements can only be reliably estimated from the clinical situation and basic cardiovascular parameters on about 50% of occasions and that the reliability of the estimation does not vary between groups with different left ventricular performance.