This study will compare two ultrasound techniques, 2D and 3D speckle-tracking echocardiography, for measuring how well the heart muscle contracts in patients with heart failure and reduced pumping function. While 2D global longitudinal strain (GLS) is widely used and has proven value in predicting outcomes, 3D GLS may provide a more complete assessment of heart function. Researchers will enroll 419 patients from seven cardiac rehabilitation hospitals in Italy and analyze heart ultrasound images using standardized equipment and software. The study will assess how closely 2D and 3D GLS measurements agree, identify factors that influence any differences, and determine whether 3D GLS better predicts the risk of death than 2D GLS.