Abstract Cardiac output is the amount of blood ejected from the ventricles with each cardiac cycle. The pulmonary artery catheter has been the mainstay in assessing cardiac output for decades. Its routine use carries potential risks of right ventricular perforation, pulmonary artery rupture, and/or embolization. Echocardiography, esophageal Doppler, transpulmonary thermodilution, and pulse wave analysis are alternative methods to assess cardiac output. To properly assess the cardiac output in surgical and critically ill patients, it is of great importance to become familiar with the chosen technique and its pitfalls. Nevertheless, estimating the cardiac output in patients is important for anesthesiologists and intensivists in order to ensure adequate oxygen delivery and tissue perfusion.