Background: The extracellular matrix tissue of the myocardium importantly contributes to left ventricular (LV) performance. Inherited connective tissue disorders related to the FBN1 gene could involve cardiac interstitium resulting in functional abnormalities.Hypothesis: To disclose a primary involvement of myocardium, LV function was studied in 28 patients affected by Marfan syndrome or Marfan-related disorders: 20 Marfan and 8 MASS (Mitral valve prolapse, Myopia, Aortic dilatation, Skeletal involvement, Skin striae) and in 28 healthy, age and gender-matched controls. No valvular regurgitation or any other cardiac alterations were present.Methods: Echocardiographic study was performed to investigate LV systolic and diastolic function.Results: No statistically significant differences were observed between patients and the control group in LV dimensions, systolic function parameters (ejection and shortening fraction), and some diastolic function parameters (E peak, A peak, E/A), while statistically significant differences were found between patients and the control group in LV mass (128.7 ± 46.6 vs. 83.7 ± 14.5 g/m2, p < 0.008), in isovolumic relaxation time (102.0 ± 24.0 vs. 80.1 ± 11.2 ms, p<0.016), and in deceleration time of the E wave (127.5 ± 19.3 vs. 208.6 ± 24.5 ms, p < 0.001) and the A wave (66.4 ± 8.2 vs. 87.5 ± 23.4 ms,p< 0.008).Conclusions: These data show an unusual pattern of transmitral diastolic flow in which a decreased ventricular compliance and reduced myocardial relaxation coexist. Thus, in Marfan syndrome and in Marfan-related disorders, subclinical diastolic alterations are present independent of valvular disease and might represent an early marker of primary myocardial involvement.