Hypoplastic left heart syndrome describes a spectrum of cardiac anomalies characterized by hypoplasia of the left heart including hypoplasia, stenosis or atresia of mitral and aortic valve as well as hypoplasia of the ascending aorta and aortic arch. The diagnosis of HLHS is established by 2D echo in the precordial views showing hypoplasia of the left ventricle as well as hypoplasia, stenosis or atresia of the mitral and aortic valve. Hypoplasia of the ascending aorta and the aortic arch can be displayed from the high parasternal and suprasternal window. Colour Doppler is helpful to discriminate stenosis of the mitral and aortic valve from atresia. Retrograde perfusion of the aortic arch and of the ascending aorta can be displayed from the suprasternal window. Colour Doppler interrogation is important to confirm unrestrictive patency of the ductus arteriosus and to assess the size of the interatrial communication. The shunting pattern across the ductus arteriosus can be displayed by PW and CW Doppler, revealing possible gradients if the ductus arteriosus becomes restrictive. Restriction of the interatrial communication is confirmed by PW and CW Doppler interrogation of left to right shunting showing acceleration of flow and transition from phasic to continuous flow pattern.