Recent studies have demonstrated that cardiac resynchronization therapy diminish morbidity and mortality of patients with heart failure, who remain symptomatic despite an optimal medical treatment and who have a wide QRS. However, 30% of patients are non-responders. Hence, echocardiography constitutes an interesting tool for the diagnosis of asynchrony. Different echocardiographic indices predict response to cardiac resynchronization therapy. In this article, a practical approach is proposed for these patients.