Recent studies have shown markedly reduced functional capacity in long-term survivors of ventricular septal defect (VSD), and in order to explore possible mechanisms, we performed non-invasive assessment of ventricular force-frequency relationships during exercise in adults operated for VSD in early childhood. We conducted a prospective study at a tertiary referral center. Patients (n=23) and healthy controls (n=20) underwent continuous Doppler-echocardiographic imaging during supine bicycle ergometry. The cycling workload was individually and manually incremented during the test session in response to heart rate. The heart was imaged in an apical 4-chamber view, and color-coded myocardial velocities were recorded. Post hoc, peak systolic velocity and isovolumetric acceleration (IVA) were blindly determined in the basal ventricular segments. VSD-operated patients differed markedly in all right ventricular endpoints compared with controls. IVA was lower prior to the test, 70 ± 30 cm/s(2) vs. 150 ± 60 cm/s(2) among controls, and during the entire test session ending at a heart rate of 160 beats/min; 140 ± 50 cm/s(2) vs. 300 ± 30 cm/s(2), p < 0.01 at both points. A similar pattern was revealed in terms of peak right ventricular systolic velocity. Left ventricular and septal measurements showed a similar, although less significant, tendency with a clearly lower left ventricular optimum heart rate among patients: 140 beats/min vs. 154 beats/min among controls. In the diseased cohort biventricular force-frequency relationships were directly correlated to peak oxygen uptake. VSD repair in early childhood is associated with disruption of the right ventricular force-frequency relationship, which may contribute to the previously observed reduction in functional capacity.