BackgroundCardiac arrhythmias, especially ventricular tachyarrhythmias are an important public health problem. QT dispersion (QTd), defined as the difference between maximal and minimal QT intervals, reflects the regional inhomogeneity of ventricular repolarization dispersion and may mark the presence of malignant ventricular arrhythmias. Purpose To determine the effects of Pranayama (breathing exercise) on QTd in patients with arrhythmia. Patients Fifteen patients with arrhythmia and ejection fractions <40% (mean = 28 ± 9%) who were on a stable medical regimen. Design and Intervention Standardized 12-lead surface ECGs were obtained at the beginning and end of the Pranayama session, and QT and JT intervals were measured manually and corrected for heart rate by using Bazett's formula. QTd, heart rate-corrected QTd (QTc-d), JT dispersion (JTd), and heart ratecorrected JTd (JTc-d) were measured in at least eight ECG leads in each patient. Results Following the Pranayama session, patients with arrhythmia had only slight improvements in exercise capacity (results were not significant). However, these patients had marked improvements in QTd (71 ± 11 to 59 ± 17 ms; P < .02), QTc-d (82 ± 28 to 63 ± 17 ms; P < .01), JTd (76 ± 19 to 57 ± 18 ms; P < .002), and JTc-d (84 ± 23 to 61 ± 18 ms; P < .001) following the Pranayama session. Conclusion These data indicate that Pranayama significantly reduces the indices of ventricular repolarization dispersion in patients with arrhythmia. Further studies are needed to evaluate how effectively this reduction in ventricular repolarization dispersion decreases the risk of malignant ventricular arrhythmias and sudden death in patients with arrhythmia.