Background: Weaning failure is defined as failing spontaneous breathing trial or developing post-extubation respiratory distress that requires re-intubation or non-invasive ventilation within 48 h following extubation. Identification of reliable predictors of weaning failure may represent potential avenues of treatment that could reduce the incidence of weaning failure. Known predictors of weaning failure include chronic obstructive airway disease, cardiac failure, positive fluid balance and diaphragmatic dysfunction. Aim: To assess the usefulness of heart, lung & diaphragmatic ultrasound in prediction of weaning failure in critically ill patient and to compare it with conventional predictors of weaning. Patients and Methods: a prospective observational study conducted on 40 critically ill ventilated patients and admitted to the critical care department where heart, lung & diaphragmatic ultrasound were done for adult patients who were intubated and mechanically ventilated for at least 48 hours and ready for weaning according to the readiness criteria. Results: According to weaning outcome in the initial SBT, patients were divided into 2 groups: Successful weaning group (Group A):  included 18 patients who had successful weaning during SBT. Failed weaning group (Group B):   included 22 patients. The failing group had higher B-line score (2.5±0.7 vs. 1.6±0.6), P = 0.002. Successful group had higher diaphragmatic excursion (2±0.4 vs. 1.2±0.5 cm, P <0.001). Diastolic dysfunction more than grade I, could predict weaning failure with sensitivity 100%, specificity 66%, PPV 78% and NPV 100% with an AUC 0.955(0.837-0.995).  Conclusion: Failed weaning in mechanically ventilated patients is more prevalent if markers of LV dysfunction (systolic and diastolic), B line score and reduced diaphragmatic excursion are present. Prediction of weaning failure could be significantly assisted by an integrative, dynamic, and fully bedside ultrasonographic concomitant assessment of the heart and lungs before the start of the weaning process or during SBT.