**7. Constrictive versus restrictive physiology: differences and similarities**

Clinical spectra of CP and RCM frequently overlap given the defect of diastolic ventricle filling that is common to both diseases. Anyway, as a specific treatment for each of them is present, a correct differential diagnosis is mandatory. RCM is characterized by increased myocardial stiffness and, therefore, increased ventricular filling pressures in both the systemic and pulmonary circulations with the increase of both mitral and tricuspid inflows during inspiration. Differently, CP is characterized by discordant respiratory flow variations in RV and LV (*ventricular interdependence*) (**Figure 5**), frequently accompanied by the *paradoxical pulse* sign and *septal bounce* pattern and, predominantly, by systemic venous congestion. That makes the presence of symptoms and signs of pulmonary edema and congestion more frequent in RCM than in CP. This phenomenon is also reflected by the presence of severe post-capillary pulmonary hypertension in RCM, whereas it is almost absent in patients with CP. Similarly, although both present a "square root" morphology of ventricular diastolic pressure, tele-diastolic pressures of LV and RV are usually equal in CP, whereas LV has usually a higher pressure (4–5 mmHg more) than RV in RCM [22]. Finally, from a clinical perspective, the presence of pericardial knock suggests CP diagnosis.

Moreover, non-invasive imaging modalities, like echocardiography, CT scan, and cardiac MRI, are helpful in the diagnostic process as the presence of pericardial calcifications and/or increased pericardial thickness suggest CP, whereas ventricular hypertrophy (with or without delayed gadolinium enhancement at MRI) and marked atrial enlargement suggest RCM. Finally, myocardial tethering by adhered pericardium is present in CP (absent in RCM) and is accompanied by LV shape deformations and/or reduced circumferential restoration and speckle-tracking examination with normal longitudinal restoration. On the contrary, in RCM, circumferential restoration is normal, whereas longitudinal restoration is reduced. Similarly, e'lateral is equal or slower than e'medial in CP **(***annulus reversus*), whereas it is the opposite in patients with RCM (**Figure 4**). Medial e'wave is usually normal in patients with CP (reflecting

the absence of myocardial disease), whereas it is reduced in patients with RCM (*annulus paradoxus*) [23]. Finally, in doubtful cases, endomyocardial biopsy could confirm or exclude RCM [24].
