The purpose of this study was to gather the fundamental information for prevention against drowning. Two hundred and nineteen subjects answered questionnaires. In addition, sixty four subjects ranging from junior high school students to those in their old age participated in the experimental parts of the study. In Part I, effects of apneic facial immersion on the cardiovascular system were measured by electrocardiogram (ECG) and sphygmomanometer under the conditions of 1) with the change of water temperature. 5°C, 15°C and 30°C 2) inspiratory and expiratory stages of respiration. In Part II, ECG and biochemical components of blood were monitored during 4 different swimming conditions. In Part III, effects of abrupt change of water temperature during body immersion on the cardiovascular system were measureed by ECG and sphygmomanometer. Main results were as follows;
　1. More than a few subjects were found to conduct themselves in the manner that could possibly lead to drowning.
　2. There was a good correspondence between appearance of arrhythmia during apneic facial immersion and that during swimming. Heart rate decrease and incidence of arrhythmia during apneic facial immersion were also related to the change in water temperature and expiration. These results suggest that a medical check up for swimming should include apneic facial immersion at the expiratory stage of respiration in the water of 15°C.
　3. RonT ventricular premature contraction appeared in two subjects during maximal anaerobic swimming and swimming after maximal anaerobic exercise on land. These exercise should therefore be regarded as riskful.
　4. Abrupt change in water temperature during body immersion led to elevated blood pressure and appearance of arrhythmia. Therefore, one should be very cautious when swimming in the sea or river where there may be sudden change in the water temperature.

DESCENTE SPORTS SCIENCE Vol.11/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE