The number of patients with chronic heart failure is increasing rapidly in the Western world. Despite the introduction of new pharmacologic therapies, the prognosis of these patients remains poor. Left ventricular (LV) dyssynchrony is a frequently observed feature in patients with heart failure, and is recognized as an important predictor of poor outcome if left untreated. The presence of LV dyssynchrony leads to inefficient LV contraction with a decreased cardiac output. Moreover, patients with LV dyssynchrony are at increased risk of adverse cardiac events. New therapeutic options targeted at restoring normal mechanical synchrony, such as cardiac resynchronization therapy, have been shown to improve clinical symptoms and prognosis in patients with heart failure. The beneficial effects of cardiac resynchronization therapy are predominantly mediated by this treatment's ability to reduce LV dyssynchrony. Given these results, adequate identification of LV dyssynchrony in patients with heart failure is of paramount importance. Several new imaging techniques are proving useful for diagnosis of LV dyssynchrony. In particular, advanced echocardiographic techniques (e.g. tissue Doppler imaging) and conductance catheter techniques are two accurate methods for quantification of LV dyssynchrony. In this review, we discuss the pathophysiology, diagnosis and treatment of LV dyssynchrony in patients with heart failure.