The sinus disease in children with" healthy hearts" is exceptional, and has never been documented by tracing of the sinus node. We are reporting two cases of two children, aged 4 and 14 years. An electrophysiological exploration with measurement of the direct activity of the sinus node, illustrates in one case the mechanism of sinus dysfunction. A review from the literature and our cases specifies some of the characteristics of this disease: 1) there are two forms: sporadic (case n. 1) 59 published cases, and familial (case n. 2) 28 published cases in 13 families; 2) the familial forms have a dominant autosomic transmission with variable penetration; 3) the disease may occur during the first days of life, suggesting a congenital origin (from the pathology findings, this disease may be one of the causes of the unexplained sudden death syndrome in infants; 4) association to atrio-ventricular conduction disorders and atrial and ventricular rhythm disorders; 5) frequent indication of stimulators, emphasizing the severity of this disease with a more severe course in sporadic forms (7 deaths in 59 cases).