Two cases of severe hypertrophic obstructive cardiomyopathy in the neonate are reported. The first case was poorly tolerated because of predominant stenosis of the right ventricular outflow tract causing right to left shunting through a patent foramen ovale. The second case presented with severe syncope at 6 weeks of age. The first patient was treated with propranolol without any success. Regression of the clinical and electrocardiographic signs was obtained in both cases with lidoflazine, within a few weeks. Red blood cell calcium concentrations were abnormally high in both patients before treatment and returned to normal levels with clinical and echocardiographic improvement. Abnormal accumulation of intracellular calcium in the myocardium is a possible mechanism of this cardiomyopathy. The relation between this type of accumulation and the effects of catecholamine discharge are recalled. The possible initiating role of an enzymatic abnormality of calcium entry is discussed: the chaotic geometric alignment of the myocardial fibres, characteristic of this type of hypertrophy, would therefore be a secondary phenomenon. Once constituted, the hypertrophy would then become irreversible. However, it may be possible to reverse it in the neonate by calcium antagonists as suggested by these two cases.