Objectives:The aimof the study was to compare diffusing capacity of the lung for carbon monoxide (DLCO), and DLCO components: membrane diffusion (Dm) and capillary blood volume (Vc), between patients withleft ventricular diastolic dysfunction and healthy controls, as wellas among three groups of patients stratified according to diastolic dysfunction grade. Diastolic dysfunction is characterized bytransmission ofincreasedleft ventricular enddiastolic pressureto pulmonary microcirculation, and is associated with a significant risk of heart failure and mortality. DLCO is sensitive test in assessing pulmonary microcirculation and function of alveolar membrane. We hypothesized that changes inDLCO, KCO, Dm, Vc corelate with grade of diastolic dysfunction reflecting changesin pulmonary capillary blood volume and diffusion membrane.Patients and methods: We studied85 patients (63% females) with diastolic dysfunction, and 51 healthy controls (59% females). Patients were classified asfirst grade (50 patients), second (20 patients) and third grade (15 patients) diastolic dysfunction. Patients with abnormal pulmonary function, as well as abnormal systolic function were not included. Normal values for DLCO, KCO, Dm, Vcwere defined as ≥80% of predicted.Results: Abnormalities of pulmonary diffusion parameters were significantly more prevalent in patients than in controls. Significant differences in DLCO, Dm, Vc were observed among three groups according to grade of diastolic dysfunction; in first gradeof diastolic dysfunction there was a trend towards increased values of DLCO, KCO, Vc, in the second and third grade significantly decreased values of DLCO, KCO, Dm, Vc were registered. VIIIConclusion:Results are consistent with hypothesis of enlarged pulmonary capillary bloodvolume in first grade diastolic dysfunction, as well asprogressively decreased pulmonary capillary blood volume and diffusion membrane permeability in second and thirdgrade of diastolic dysfunction.