Background: Measurement of cardiac output helps in prompt management of hemodynamic disturbances in the perioperative period as well as in critical patients. There are various methods for monitoring of cardiac output, out of which thermodilution (PAC guided) method (PAC–CCO) is considered gold standard. We compared the purely non–invasive (esCCO) and invasive (PAC–CCO) methods of cardiac output assessment in elective coronary artery bypass grafting (CABG) cases. Methods: In this prospective observational study of 6 months duration, 35 patients posted for elective CABG at our centre were studied. Results: Out of 498 datasets obtained, there were same readings in only 5 datasets. 135 datasets gave lower estimation and 358 datasets give higher estimation. The mean values for cardiac output in invasive and non–invasive cardiac output were 4.4 and 4.97 lit/min (mean statistically significant difference of 0.57 lit/min). The datasets showed significant correlation between invasive and non–invasive cardiac output (p<0.001, r = 0.72). Conclusion: Cardiac output assessed with non–invasive method showed higher as well as lower estimates, but chances of higher estimates are more. The non–invasive (esCCO) method of cardiac output estimation showed strong correlation with gold standard Invasive (PAC–CCO) method.