Background: Cardiac output (COP) monitoring is a cornerstone in the management of critically ill patients. Objectives: to assess the validity of Capstesia^TM app for COP monitoring compared to the traditional echo-based velocity time integral (VTI) technique in hemodynamically unstable patients. Patients and Methods: In prospective cohort study, 50 cases were admitted with shock state and candidates for continuous COP monitoring. Readings obtained from 50 patients were measured simultaneously by Capstesia^TM app and VTI method. Results: The mean age of participants was 63±11 years, 29 patients were males, and 33 patients suffered from septic shock. With a p-value of 0.76, the two methods that were compared did not differ from one another in a way that is statistically significant, the level of agreement between the two methods was least in chronic kidney disease (CKD) patients. Conclusion: Smartphone application Capstesia^TM is a reliable alternative to the traditional echo-based VTI technique in continuous COP monitoring in hemodynamically unstable patients.