A total of 75 patients with proved weak sinus node syndrome (WSNS) were examined. In many cases, WSNS was found to accompany cardiovascular diseases, such a coronary disease, myocarditic cardiosclerosis and essential hypertension. Sinus node dysfunction is often combined with signs of disorder in other departments of the hearts conductive system. A screening for WSNS should incorporate a combination of diagnostic procedures, of which Holter's ECG monitoring and electrophysiological investigation of the heart's conductivity are the most reliable and informative.