Risk strati cation is required to set an exercise prescription for cardiac rehabilitation, but an optimal scheme for congenital heart disease (CHD) is unknown. We piloted a system based on hemodynamic rather than anatomic factors: Function, Oxygen level, Rhythm, Complex/Coronary anatomy, and Elevated load (FORCE). Feasibility, e cacy, and safety of the FORCE tool were evaluated.Methods: Patients <22 years old participating in the Cardiac Fitness Program at Boston Children's Hospital between 02/2017 and 12/2021 were retrospectively analyzed. Assigned FORCE levels, anatomy, adverse events, tness and exercise test data were collected.Results: Of 63 attempts at FORCE classi cation, 62 (98%) were successfully classi ed while one with restrictive cardiomyopathy was not. Thirty-nine (62%) were FORCE 1, 16 (25%) were FORCE 2, and 7 (11%) were FORCE 3. Almost half of FORCE 1 patients had simple or complex CHD and the majority of FORCE 2 patients had single ventricle CHD. FORCE 3 patients were more likely to have serious arrhythmias or cardiomyopathy than those in FORCE 1 or 2 (p<0.001). Postural orthostatic tachycardia syndrome patients appeared in FORCE 1 only. No adverse events occurred over 958 total sessions. The total number of tness sessions/participant was similar across FORCE levels. Conclusion: It was feasible to risk stratify patients with CHD using a clinical FORCE tool. The tool was effective in categorizing patients and simple to use. No adverse events occurred with tness training over nearly 1,000 exercise training sessions. Adding diastolic dysfunction to the original model may add utility.