Heart rate and R-R intervals of ECG during sleep were examined in healthy young men. Heart rate per minute were gradually decreased when the subject fell asleep. Whole through one night sleep data there were two typical heart rate variation patterns, namely stable stage and fluctuating stage. Sleep stages determined by EEG, EOG and EMG of chin corresponded with these two patterns; slow wave stage (Stage III/IV) showed the stable pattern, REM Stage and Stage I showed the fluctuating pattern, Stage II both patterns. The fluctuating pattern showed higher heart rate level.
Further studies computed R-R intervals and its variations of ECG revealed 4 typical patterns on the variations, and well corresponded with sleep patterns determined by the above methods. R-R interval varied from 1.39 to 0.67 sec during sleep. R-R interval variation befor onset of sleep showed lightly rythmical periodicity (20-40 sec) and small fluctuation (0.1 sec) (awaking pattern) . R-R intervals after onset of sleep extended gradually, fluctuating midly (0.1 sec) and did not show any periodicity (transient pattern) . R-R interval reached its maximum level then. At slow wave stage (S-III/IV) R-R interval showed mild fluctuation as the transient strage, and did not show any periodicity (stable pattern) . At REM stage and S-I it showed large fluctuation (more than 0.2 sec) and significant periodicity (10-30 sec) . At S-2 if the stage was in the course of deepening the sleep, it showed stable pattern and if it was in the course of lightening the sleep it showed fluctuating pattern.

We describe our experience with a left atrial (LA) myxoma in a 15-year-old female who experienced abdominal symptoms so prominent that she was initially thought to have an inflammatory enterocolitis.
The patient's young age and predominant abdominal symptoms in the absence of any cardiac symptoms made it difficult to diagnose the LA myxoma early in the present case. This experience underscores the need for an intensive search for cardiac myxomas in patients with findings suggestive of inflammatory diseases or collagen disorders.