Background and Objective : The Valsalva maneuver (VM) affects the cardiovascular system by mechanical and reflex mechanisms. These effects are different in each of four phases of (VM) and may cause opposite changes. The ECG manifestations of (VM) are not fully reported and is the main focus of this study.

  Material and Methods : This self-control clinical trial study was conducted in 20 healthy male college students (20.12±2.23 years). They were well trained to perform (VM) in standard mode e.g. the maintenance of 15 second expiratory pressure at 40 mmHg with open glottis. At (1) basal condition, (2) the start and (3) late strain in second phase of (VM) , the ECG was recorded in supine position and lead II was used for software analysis of time (ms) and voltage (mv) changes. The averages of four successive beats were computed and mean±S.E.M were used for data comparison by paired T-test.

  Results: Following (VM), the RR and PR intervals are significantly lower than baseline during phase two and three of (VM) (p<0.05). QT has no changes but the corrected QT interval is increased in phase two and three, in comparison with basal condition (p<0.05). The P wave duration shows significant changes, just in the beginning of strain phase (phase II). The QRS duration does not show significant changes in all phases of (VM). The P wave amplitude is increased in two and three (p<0.05). The R wave amplitude does not show significant changes in two and three in comparison with phase one , but is lower in three than two (p<0.05). The T wave amplitude is decreased in two and three it also is significantly lower in three than two. The ratio of T/R amplitude in two and three is less than baseline (p<0.05).

  Conclusion: The second phase of (VM) results in some changes in time and amplitude of ECG waves. Because of relative stability of hemodynamic responses in phase II of (VM), it seems that R,T and P changes are caused by factors such as lung volume and autonomic tone rather than Brody’s effect.