Introduction: Cardiac axis is altered in many physiological and pathological states. Hence its measurement is important. Position and movements of diaphragm determine the position of heart because the pericardium is firmly attached to the central tendon of the diaphragm. Effect of change in body posture and breathing on cardiac axis has not been well documented. The changes in cardiac axis during deep breathing are greater in aged patients. Aim: To study the effect of deep breathing on cardiac axis of young normal subjects in various postures. Materials and Methods: This was a cross-sectional study done on 45 normal healthy volunteers. After 10 min of supine rest, with the help of INCO RMS Vesta 101 electrocardiograph, ECG was recorded in leads I and aVF during eupnea, after maximum inspiration and after maximum expiration. The measurement was repeated in sitting and standing postures. The cardiac axis was calculated from Einthoven triangle. Data was analysed using ANOVA and inter-group was analysed using post-hoc test. Results: Maximum inspiration produced a significant (p<0.001) increase in cardiac axis as compared to eupnea, in supine, sitting and standing postures. Maximum expiration produced a significant decrease in cardiac axis as compared to eupnea only in sitting (p=0.05) and standing postures (p=0.01). Conclusion: Cardiac axis varies with posture as well as breathing. Maximum inspiration produces significant increase in cardiac axis whereas maximum expiration produces an insignificant decrease.