Aim: Studying LV dysfunction during weaning from mechanical ventilation (MV).Methods:30 invasively MV patients fulfilling criteria of weaning and shifted to SBT (using low PSV (8 cmH2O)) for 30 minutes.2 sets of variables were measured at the beginning and end of the SBT; respiratory rate (F),tidal volume (VT),minute ventilation(VE), peak inspiratory pressure (PIP), PaO2/FIO2 ratio(P/F ratio) and one reading at the start of the SBT of; Airway resistance (Raw),static respiratory compliance (Ceff), maximum negative inspiratory pressure (NIP), (F/VT),Arterial blood gases. Weaning failure was defined as; Failed SBT, Reintubation and/or reventilation or death within 48 hours. Swan Ganz catheterization was done to get the right atrial (RAP), pulmonary artery (PAP), pulmonary artery occlusion (PAOP) pressures, and cardiac index (CI). Echocardiography to get LV internal diameter at end diastole (LVIDd) and end systole LVIDs), Ejection fraction (LVEF), E/A ratio, Deceleration time (DT)(ms) Isovolumetric relaxation time (IVRT), Doppler tissue imaging (DTI) and E/E`.Results:Mean age 56.6 ±15.9y 53% were males. Weaning was successful in 76.6% of patients. There was reduction in VT with increase in f andVE; (0.53±0.06 vs. 0.45±0.1 L, p=0.0003), (12.5±2 vs. 20.3±7.5,p<0.0001),(6.6±1.5 vs.8.8±2.4 L,p<0.0001) respectively, P/F_1was higher than P/F_2 ;( 278±86 vs. 252±74, p=0.005).ABG showed reduction in PaO2 (126±32 vs. 115±29, p=0.01) without change in PaCO2 (37.6±6.4 vs. 36.5±6.2, p=0.24). There was rise in PAOP with insignificant change in RAP, PAP, and CI (12.6±4.7vs.14.2±4.7, p=0.003),(6.6±2 vs. 7.2±3, p=0.16), (29.7±7.2 vs. 29.7±7, p=1),(3.2±0.6 vs. 3.22±0.5, p=0.4) respectively. There was reduction in LVEF with insignificant LVIDd and LVIDs change (66.4±8.1 vs. 64.5±8.4%, p=0.01), (4.83±0.68 vs. 4.7±0.7, p=0.5), (3.1±0.7 vs. 3.12±0.6 cm, p=0.8) respectively. There was no differences between E/A, IVRT, and DT or E/E' at both ends of the trial (1.02±0.38 vs. 1.04±0.37, p=0.6), (95.5±24 vs. 95.8±22, p=0.8),(194.6±30 vs. 195±28 ms, p=0.8) and(9.7±3.1 VS. 10.3±3.5, P=0.09) respectively/E' and RAP correlated significantly before and after SBT(r=0.54, p=0.002), and (r=0.79, p<0.0001) respectively. Despite insignificant correlation between E/E' and PAOP at the beginning of SBT, there was significant correlation between them at the end of SBT (r=0.6, p=0.001). Conclusions:LV dysfunction during weaning is mainly diastolic. Changes in E/E' and RAP and/or PAOP may be most convenient methods for monitoring diastolic function during weaning from MV.