Abstract: A method and apparatus determines continuously mean cardiac output by measuring the arterial pressure e.g. at a finger and calculating therefrom the mean arterial pressure and the time constant of the arterial system (in diastole). Compliance values are provided from a table. Mean cardiac output is then the product of mean arterial pressure and compliance divided by the time constant. Changes in cardiac output can be used for diagnostic purposes. A pressure cuff or pressure tonometer can be used to measure the arterial pressure with a microcomputer providing the necessary calculations.