**3.1. Right heart failure**

Right heart failure (RHF) is a syndrome reflecting the inability of the RV to fill or eject properly. Clinically, it manifests as fluid retention (peripheral edema) and decreased systolic reserve or cardiac output, which often presents as exercise intolerance [47]. In the case of RV geometry, the ventricle becomes more concentric, and the interventricular septum flattens. In humans, right heart failure is diagnosed through a combination of clinical findings, laboratory tests and imaging. Similarly, in larger animal models of RV failure (below), it can be measured by echocardiography, whereas in mouse models it is generally demonstrated by morphometric changes including RV/LV ratios and myocyte size.
