On the basis of the personal experience of 36 patients with sick sinus syndrome, the role of length, seat, frequency of atrial stimulation (AS) on the duration of correct sinus node recovery time (CSNRT) were examined. The length of AS has little importance for values over 2 minutes. In 2 cases the CSNRT were pathological only if the position had been changed from the lateral wall of the right atrium to the middle right atrium. The frequency of AS is very important for the duration of pathological and maximal CSNRT. Therefore it is better to give every patient the major range of frequencies of AS as for a correct quantitative determination of sinus dysfunction so as not to lose some falsely negative results.