Introduction: Brain natriuretic peptide (BNP) is an important marker for the evaluation and detection of the left ventricular systolic dysfunction. It seems that physical activity and circadian rhythms are effective in the changes of BNP concentration. Regarding this, the aim of the present study was to investigate the acute effects of low-volume high-intensity interval aerobic exercises in the morning and evening on BNP changes and double product in active men.
 
Materials and Methods: This study was conducted on 11 male physical education students of Jahrom University, Jahrom, Iran. The study population was selected using the purposive sampling technique. The participants were subjected to two separate sessions (with an interval of 3 days) of low-volume high-intensity aerobic exercise in the morning and evening. Blood samples were collected before and immediately after every activity both in the morning and evening. Data analysis was performed in SPSS software (version 17) using independent t-test to compare the mean pretest and posttest upon each session and obtain the mean difference between the morning and evening data. P-value less than 0.05 was considered statistically significant.
 
Results: The results showed that BNP concentrations increased after exercise in the morning and evening; however, this increase was not statistically significant (P>0.05). In addition, the results showed that the double product in the morning and evening significantly enhanced after performing the exercises (P=0.001). There was a significant difference between the BNP concentrations obtained in morning and evening in terms of double product (P=0.035).
 
Conclusions: Despite the lack of a significant difference between morning and evening BNP concentrations, due to the lower mean concentration of BNP in the evening, it seems that exercise in the evening exerted less stress on the myocardial wall and could be more appropriate.