BackgroundThe main determinants of diastolic function—pre-and afterload of the heart—are affected by the haematocrit, but the relation between haematocrit and diastolic function is unclear.ObjectiveTo study the association between interindividual haematocrit values and diastolic function, by echocardiography.DesignIn a cross-sectional survey, blood pressure, haematocrit values, and high-quality Doppler indexes of left ventricular filling were obtained in 1297 individuals, 25–74 years of age, and analysed by regression analyses.ResultsHaematocrit and systolic blood pressure were strongly correlated (r= 0.23;P< 0.0001). Moreover, haematocrit was inversely correlated with the peak velocity of early left ventricular filling and with the peak velocity of early filling divided by late filling (E/A ratio; bothP< 0.005). Left ventricular isovolumic relaxation time (IVRT) was positively associated with haematocrit (r= 0.18,P< 0.001). In individuals with an abnormal Doppler filling pattern (E/A<50 years< 1, E/A> 50years< 0.5, or IVRT< 30years> 92 ms, IVRT30–50years> 100 ms or IVRT>50 years> 105 ms;n= 119), greater haematocrit values were observed than in those with normal diastolic parameters (P< 0.001). Conversely, individuals with an increased haematocrit (> 50% in men, > 45% in women;n= 16) had a greater risk of presenting with abnormal left ventricular filling (31.3%) compared with individuals with normal (12.1%;n= 898;) or low (< 40% in men, < 35% in women: 10.5%,n= 38;P= 0.07) haematocrit. Strong and significant associations between haematocrit and Doppler indexes of left ventricular filling were confirmed after adjustment for multiple potential confounders including blood pressure, antihypertensive medication and body mass index. Similarly, blood pressure and parameters of diastolic filling were strongly associated correlations that were not affected by inclusion of haematocrit values into the regression model.ConclusionThe data point to substantial adaptations of diastolic filling in response to both blood pressure and the characteristics of the medium that is propelled by the heart. Therefore, in addition to blood pressure values, the variability of haematocrit values should be considered when diastolic function is being evaluated by Doppler echocardiography.