Abstract: A method for continuously determining cardiac output (CO) in a subject comprising continuously measuring arterial blood pressure data at a site and converting said arterial blood pressure data to a digital signal representative of a pulse contour curve waveform, calculating heart rate, grade of slope, systolic peak pressure, the presence of reflected waves, and pressure at the dicrotic notch from said digital signal; determining the area, SA, under said pulse contour from the start of a pulse to the dicrotic notch of said pulse contour curve; for any pulse which is reflective, subtracting from said area A any portion, B, of said area A, representing an approximate area due to wave reflection to obtain a stroke area, SA; and calculating CO as a product of SA and HR. Apparatus for continuously determining cardiac output (CO) in a subject comprising means for carrying out each step of the method are also disclosed.