Introduction. Cardiac reserve could be defined as the spontaneous magnitude from basal to maximal cardiac power under stress conditions. The aim of this study was to evaluate the prognostic value of cardiac reserve parameters in resuscitated septic shock patients. Methods. Seventy patients with septic shock were included in a prospective and observational study. Prior to inclusion, patients were resuscitated to reach a mean arterial pressure of 65–75 mmHg with an euvolemic status. General, hemodynamic, and cardiac reserve-related parameters (cardiac index, double product, and cardiac power index) were collected at inclusion and at day 1. Results. Seventy patients were included with 28-day mortality at 38.5%. Ten of the 70 patients died during the first day. In multivariate analysis, independent predictors of death were SAPS II ≥58 (OR: 3.36 [1.11–10.17]; P = 0.032), a high double product at inclusion (OR [95% IC]: 1.20 [1.00–1.45] per 103 mmHg·min; P = 0.047), and at day 1, a decrease in cardiac index (1.30 [1.08–1.56] per 0.5 L/min/m2; P = 0.007) or cardiac power index (1.84 [1.18–2.87] per 0.1 W/m2, P = 0.008). Conclusion. In the first 24 hours, parameters related to cardiac reserve, such as double product and cardiac index evolution, provide crucial and easy to achieve hemodynamic physiological information, which may impact the outcome.