This study was carried out among 120 Navy soldiers included 70 surface ship soldiers and 50 submarine soldiers in order to investigate the cardiovascular strain of navy soldiers. The subjects were recorded 100 rate - rate of electrocardiograph at Dlliead in order to calculate the heart rhythm statiscal mathematical indeces before and after 15 days of working at sea. The results showed that, after 15 days of working at sea, there were significant inceases in tense index and rate of dominant sympathetic tone in comparison with that before working at sea that demonstrated the cardiovascular strain among navy soldiers. After 15 days of working at sea, 0 index was lower and tense index and the rate of dominant sympathetic tone were higher in submarine soldier than that in surface ship.