Prospective, multicenter, observational study to enroll consecutive patients with functional tricuspid regurgitation (FTR) with the primary aim to: * Use patients' outcomes as a reference to try to define the threshold values for the different grades of FTR severity; and secondary aims to: * Use 3D echocardiography to assess the relationships among the geometry (size and shape) of the right ventricle, right atrium, tricuspid annulus, and tricuspid leaflets according to the underlying cardiac condition (i.e., atrial fibrillation, pulmonary hypertension, right ventricular cardiomyopathy, congenital heart diseases, etc.) * Assess the accuracy, and incremental diagnostic and prognostic value of a new software package to measure tricuspid annulus and valve geometry * Develop new parameters of FTR severity that take into account the lower momentum of the tricuspid regurgitant jet (compared with the mitral regurgitation jet), the complex anatomy of the regurgitant orifice, and both the intra-beat and respiratory variation of the regurgitant volume * Test the hypothesis that there is no actual grading but a continuum of increased risk of adverse outcome with the increase of FTR severity, and we need robust quantitative metrics (for example, the regurgitant fraction - currently not included in guidelines - which takes into account the right ventricular volume and function) more than grading schemes to assess the severity of the diseases and the effect of treatments * Test the hypothesis that the relationship between FTR severity and the outcome may be different according to the underlying cardiac condition (i.e., atrial fibrillation, pulmonary hypertension, right ventricular cardiomyopathy, congenital heart diseases, post-cardiac surgery, etc.) as this will affect the timing for interventions