BACKGROUND Implantable sensors that monitor haemodynamics over time may be useful in patients with heart failure. This multicentre study assessed the feasibility of a system that has one sensor measuring absolute pressure and another measuring mixed venous oxygen saturation (SvO(2)). Both sensors were mounted on leads that were implanted in the right ventricle. METHODS Twenty-one patients with heart failure (NYHA II-III) were included. Comparisons were made to right heart catheterizations at implant and at 2, 6 and 12 months thereafter. Patients underwent several haemodynamic provocations during the catheterizations. RESULTS Overall, among functioning sensors, the IHM-1 values were highly correlated with reference values for all time points during all provocations, demonstrating high reproducibility and stability (r(2)=0.91, 0.79 and 0.78 for systolic, right ventricular diastolic and SvO(2), respectively). Although IHM-1 underestimated reference pressure values by 4.5 mmHg and SvO(2)by 1.6%, this difference was consistent across provocation and stable over 12 months of follow-up. Twelve of the 21 oxygen sensors failed to function and two pressure sensors had component failures. Preliminary analysis of long-term data revealed haemodynamic patterns that may be key indicators for therapeutic interventions. CONCLUSIONS This multicentre feasibility study demonstrated the accuracy and stability of sensors implanted in the right ventricle. The IHM-1, using right ventricular pressures and SvO(2), with improved performance, might be useful in the study of pathophysiological mechanisms and treatment interventions in heart failure.