The pulse contour method is one of the technologies used for min-invasive monitoring of CO. It is based on the relationship between arterial blood pressure and stroke volume and has been greatly improved since early 1950s. Arterial waveform-based CO is frequently used in current medical practice, but it still requires arterial puncture. Pulse wave transit time has been proven to have good correlation with stroke volume. Pulse wave transit time consists of a pre-ejection period, pulse wave transit time through the artery, and pulse wave transit time through the peripheral arteries, which compensates for the effect of changes in systemic vascular resistance (SVR). Based on the relationship between pulse wave transit time and stroke volume, the noninvasive device, estimated CCO (esCCO), via measuring electrocardiogram (ECG), pulse oximeter wave, and arterial blood pressure had been developed by Sugo et al.. It has the great advantage to simplify CO measurement by combining the results of these familiar noninvasive monitoring techniques. Thus, it may be a useful technique for optimizing medical treatment.