The general purpose of this thesis is to establish the ability of Speckle Tracking Echocardiography (STE) in assessing left atrial (LA) response to pressure and volume overload respectively in aortic stenosis (AS) and mitral regurgitation (MR), and to evaluate its accuracy in predicting LA and right ventricular (RV) fibrosis in patients with end-stage heart failure (HF) undergoing heart transplantation (HTx). I demonstrated that assessment of left ventricular (LV) long axis systolic velocity and amplitude of excursion is more sensitive than simple determination of ejection fraction (EF) for revealing the beneficial impact of MR surgery on overall LV systolic performance. Severe symptomatic AS is associated with LA enlargement and compromised mechanical function with a high incidence of peri-operative atrial fibrillation (AF). Valve replacement reverses these abnormalities and regains normal atrial function, a behaviour which is directly related to the severity of pre-operative LV outflow tract obstruction. Early identification of LA size and function disturbances, as shown by myocardial strain measurements might contribute to better patient’s recruitment for a safe valve replacement. In late stage HF patients, the right ventricle is enlarged, with reduced systolic function due to significant myocardial fibrosis. RV free wall myocardial deformation is the most accurate function measure that correlates with the extent of RV myocardial fibrosis and functional capacity. In patients with preserved EF, severe MR masks LV and LA myocardial dysfunction and correlates with symptoms and post-operative cavity function instability. Three months after MVR, the underlying myocardial disturbances are unmasked suggesting that most pre-operative measurements are subject to loading conditions. Finally LA volume and PALS remain the main predictors of post-operative AF, thus should be used for stratifying surgical risk. STE has been shown to accurately determine the severity of impairment of LA myocardial function shown by suppressed PALS which was the strongest predictor of the presence and extent of fibrosis, over and above other structure and function parameters. These findings may assist in better stratifying patients with end stage HF and identifying particularly those requiring HTx.