Objective: Ventricular assist devices (VADs)are implanted in patients suffering from end-stage heartfailure to sustain the blood circulation. Real-time volumemeasurement could be a valuable tool to monitor patientsand enable physiological control strategies to provide in-dividualized therapy. However, volume measurement usingone sensor modality requires re-calibration in the criticaltime post VAD implantation. Methods: To overcome thislimitation, we have integrated ultrasound and impedancevolume measurement techniques into a cannula of an api-cal VAD. We tested both modalities across a volume rangefrom 140–420 mL using two differently sized and shapedbiventricular silicon heart phantoms, which were subjectedto physiological pressures in an in-vitro test bench. Wecompared results from standard calibrated measurementswith calculations found by a quadratic optimization for thesingle modality and their combination (dual-modality) andvalidated the results using twofold cross-validation. Re-sults: The dual-modality approach resulted in most favor-able limits of agreement (LOA) of −0.83 ± 1.54% comparedto −13.88 ± 5.90% for ultrasound and −43.45 ± 10.28% forelectric impedance, separately. Conclusion: The results ofthe dual-modality approach were as accurate as the stan-dard calibrated measurement and valid over a large rangeof volumes (140–420 mL). In this in-vitro study, we showhow a dual-modality ventricular volume measurement of ul-trasound and electric impedance increases the robustnessand renders calibration obsolete. Significance: Ventricularvolumes could be measured accurately in the critical periodpost VAD implantation despite ventricular remodeling.