## 5 Conclusions  
The designed and manufactured test stand makes it possible to investigate the pumping of artificial blood in a model system with an artificial heart, using a set of ventricular and valve balloons. Moreover, the stand ensures that the parameters of the heart have similar values to those of a human heart. It is possible to study different states of work, at different frequencies of operation. On the realistically reconstructed geometry of the heart, it is possible to reproduce conditions typical of patients with stage D heart failure accompanied by residual mitral regurgitation and thus pulmonary hypertension. It is also possible to measure pressures for different flow rates, which are generated by a portable pumping system at different operating frequencies. The studies conducted show that increasing the flow resistance increases the pressure in the heart chambers and decreases the flow rate.  
Most importantly, the innovative implantable device, in the form of a set of two balloons for left ventricular support, is able to increase the stroke volume into the aorta  
Figure 12: Experimental results for different cycles per minute—aortic, atrial, ventricular, and balloon pressure distributions (additional resistance).  
through the aortic valve during the systolic phase and to occlude or completely replace the mitral valve. In addition, balloon sizes can be adjusted to match the size of the individual heart chambers. The pulsatile action of the balloons is forced by a suction-discharge device, part of a portable pumping system, and is controlled by a control system in the form of an ODROID computer, which ensures synchronization according to the heart cycle through ECG measurements and continuous processing. Finally, the design of the device allows it to be implanted into the heart chamber in a folded state through the heart apex by means of a minimally invasive implantation. This permits a significant reduction in hospitalization time, even for patients with end-stage heart failure associated with mitral regurgitation and pulmonary hypertension.  
R.J.: conceptualization; methodology; data curation; visualization, investigation, validation. K.T.: conceptualization; formal analysis; methodology; supervision; project administration; investigation; writing--original draft. L.D.: conceptualization; methodology; data curation; visualization, investigation. J.R.: conceptualization; methodology; medical supervision. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Centre for Research and Development, Poland, POIR.01.01.01-00-1026/18.  
This study was executed in strict accordance with the recommendations for Good Clinical Practice. The protocol was approved by the Independent Bioethical Committee with the permission number NNKBN 167/2017.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
The data presented in this study are available on request from the corresponding author.  
The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this article.