Misasa Hot Springs water contains 4.81-1169.2×10(-10) curie per liter of radon and its temperature ranges from 53.0℃ to 76.0℃. The authors examined one group of 265 residents who are living over 1 year at Misasa Hot Springs and another control group of 226 residents at the middle district of Tottori Prefecture, where the Misasa area is singular for its high radon concentration. A living environment of these two groups is of same condition, for example, dietarily or economically. The incidences of abnormal ECG findings and hypertension in the both groups was analysed stochastically and the results obtained were as follows: 1. The incidences of abnormal ECG findings were found less in the residents at the radioactive hot springs area than another residents at the middle district of Tottori Prefecture. 2. The difference in these incidences were found especially about the ECG findings due to functional disorderes, for example, sinus tachycardia and bradycardia, premature supraventricural and ventricural systole, atrio-ventricural block and right bundle branch block. 3. The ECG findings due to organic disorderes, for example, both auricural and ventricural hypertrophy or strain, myocardial and coronary arterial lesions, auricural fibrillation and left bundle branch block, were not found different significantly between both groups. 4. No difference of the incidences of the functional and organic abnormal ECG findings between both aging groups, over 60 years old, were found. 5. The incidences of hypertension were not found different between both groups.