There are several methods for the determination of the cardiac output (CO), one of the most common is the thermodilution (TD) technique which consists in inserting a Swan-Ganz catheter into the circulatory system. We show results for the measurement of the CO using a noninvasive magnetic device. Methods: This protocol was carried out in two steps: A) A first step of validation (10 patients) in order to evaluate the influence of weight, height, age, or sex in the CO measurements. Those patients underwent cardiac catheterization without coronary artery disease (5 male, 5 female). B) A second step, the testing, with 35 patients who didn´t enter in the validation step, was done as follow: After placing the magnetic marker on neck subject it is right over carotid artery pulse, it was measured pressure curves every 30 seconds: 5 records for aspiratory inhalation and 5 records for aspiratory exhalation. After methodology validation, the testing step was made with two measures in each one of the subjects. Statistical analysis was made with correlation and Bland-Altman test. Results: The result of the validation step had an excellent correlation (R2 = 0.997). In the test step, 35 patients met the inclusion criteria and entered the study: 26 men and 9 women with ages between 48 and 63 years, average 57 ± 4.3 years. Cardiac output was measure a) by thermodilution 6.6 ± 1.51 L and b) with our device 7.03 ± 2.10 L. The correlation coefficient between the two methods was 0.72 (p