Aim of The Study:To find out the effect of physical exercise on platelet aggregation on normal and Ischaemic Heart Disease patients. Methodology:The present study was conducted on 50 male volunteers between the age of 40 to 60 years who were categorized in two groups of 25 each. Group 1 (n=25) Healthy group. Group II (n=25) IHD group. Venous blood sample (4 ml) was collected before and at the end of completion of stage III of Bruce protocol on the TMT and subjected for estimation of platelet aggregation on ELVI-840 aggregometer and Omniscintro chart recorder. Results:The effect of stress by Tread Mill Test (TMT) on platelet aggregation in normal individuals was a significant (P__ampersandsignlt;0.05) decrease in platelet aggregation after stress induced by ADP and collagen. . ADP induced platelet aggregation decreased which was statistically significant .Similarly collagen induced platelet aggregation also significantly decreased. The effect of stress (TMT) on Platelet aggregation in patient of Ischemic Heart Disease (IHD)- There was an increase in ADP induced platelet aggregation after stress from a mean of 47.40+12.18 to 59.79+12.43 percent which was statically significant (p__ampersandsignlt;0.001). Similarly there is also an increase in collagen induced platelet aggregation after exercise, from a mean of 39.79+11.19 to 57.30+8.79 percent. This was statistically significant (p__ampersandsignlt;0.001). Conclusion:The effect of stress (TMT) on healthy individuals reduced platelet aggregability in both ADP and collagen, showing that regular exercise helps to prevent platelet aggregation