The authors prospectively compared three techniques of continuous cardiac index measurements. They were, invasive Continuous Cardiac Index using thermodilution flow-directed Swan-Ganz pulmonary artery catheters, semi invasive Flotrac-arterial pressure derived cardiac index and the non invasive cardiac index measurement-body impedance plethsmography. The cardiac index measurements were made simultaneously in the postoperative period in 20 patients who underwent elective uncomplicated off pump coronary artery bypass graft. The values were collected once in 5 min over a period of 30-40 min. A set of 140 values were obtained from the cohorts in our study. Inter-changeability of the values of cardiac index was analysed using Bland-Altman and mountain plots. The cardiac index values ranged from 1.6 to 3.6 l/min/m(2). The values obtained were interchangeable. The bias and precision respectively were 0.02 and +/-0.06 for continuous cardiac index and Flotrac, 0.18 and +/-0.08 for Flotrac and body impedance plethysmography and 0.16 and +/-0.08 for continuous cardiac index and body impedance plethysmography. Flotrac appears to be more useful during off pump coronary artery bypass surgery.