Hypertrophic cardiomyopathy (HCM) is a frequent cardiac pathology with an estimated prevalence of 1/500 in France. The main risk factor for sudden death in this pathology is the presence and extent of left ventricular obstruction. To date, the only method allowing a reliable assessment of the extent of left ventricular obstruction is Doppler echocardiography. All patients with HCM should undergo cardiac magnetic resonance imaging (MRI) to confirm the diagnosis and for the detection of fibrosis, but conventional sequences cannot reliably assess the obstruction. 4D-flow MRI provides a complete coverage of an entire volume with the ability to simultaneously measure the outputs of all vessels within that volume in a single sequence and might be able to quantify left ventricular obstruction. The main objective of this study is to compare the quantification of left ventricular obstruction in hypertrophic cardiomyopathy by Doppler echocardiography and 4D flow MRI.