Achieving superior performance in swimming, as in other sports, depends on the customization of training for young athletes. The aim of this study was to investigate the effects of sprint interval trainings on heart rate and 50 m swimming performances of young male swimmers. 24 young male swimmers joined to the study by having their parents confirm the "Parental Permission Form". Swimmers randomly divided into two groups as normal training group and interval sprint training group. As normal training group continued the routine swimming training, interval sprint trainings (8 x 50 interval repeats in crawl and backstroke styles) were applied to the other group additionally for 8 weeks, 3 days a week, at least 30 min a day. Rested-maximum heart rate, 50 m sprint swimming test in crawl and backstroke styles were applied to the swimmers in 1st and 8th weeks of the period. The analysis of data was made in the statistical package program by using "Descriptive statistics", "Paired t Test" and "Independent t Test" for comparison. Results of pre- and post-test comparison of each group, significant differences were found in resting heart rate values of normal training group and all values of interval sprint training group (p < 0.05). Results of comparison between groups, differences found statistically significant in 8th week maximum heart rate, crawl and backstroke performances (p < 0.05). To conclude, we could say that the reason of finding significant differences in rested and maximum heart rate is the positive effects of physical activity on the cardio-vascular system (adaptation). And, the reason for the positive effects on sprint interval performance is depended on sprint interval swimming was acute origination of body's physiological reaction to rising energy need during short time and intensive physical activity even in micro plan.