Introduction: Major abdominal and thoracic surgeries have a high rate of cardiopulmonary complications and prolonged hospital stays. The Chester Step Test (CST), combined with Heart Rate Variability (HRV) analysis, may assist in preoperative risk stratification. Objective: To verify whether the CST combined with HRV can predict postoperative hospital length of stay in oncological patients undergoing non-cardiac surgeries. Methodology: Prospective study with 24 oncological patients who underwent the CST with HRV monitoring and estimated VO₂max between May 2024 and January 2025. Sociodemographic, clinical variables and length of hospital stay were analyzed using multinomial logistic regression. Results: Mean RR was associated with hospital length of stay, increasing the chance of medium-length hospitalization by 2.4% for each 1 ms increase (p = 0.031). The short-stay group presented lower HRV and higher heart rate, with breast cancer being more prevalent among women (TIH-C) and colorectal cancer among men (TIH-L). Conclusion: HRV analysis proved to be a practical and effective tool for predicting postoperative hospital length of stay, contributing to the planning and optimization of perioperative care in oncological patients.