Objective: We aimed to investigate the relation between the presence of fragmented QRS (FQRS) and exercise intolerance as assessed by 6 minute walking test (6MWT) and its association with coronary flow reserve (CFR). Methods: One hundred and twenty patients with hypertension (age: 47.3þ6.9) who were never treated and without left ventricular hypertrophy underwent 6MWT. Echocardiographic examination was obtained for all patients. CFR was calculated as the hyperemic to baseline mean velocity ratio (hyperemia was induced by intravenous adenosine 0.14 mg/kg/min). Patients were stratified into one group with FQRS and another group without FQRS. Forty-eight normotensive subjects with a mean age of 45.7þ5.3 were recruited and served as a control group. Results: The frequency of FQRS was 49% in hypertensive patients versus 2% in control subjects. Patients with FQRS had higher systolic blood pressure (p<.05; <.01), a significant lower 6MWTD (p<.001), increased LAVI (p<.05), increased E/e’ ratio (p<.01) and lower CFR (p<.001) compared with those without FQRS and controls. FQRS was inversely correlated with CFR (0.531; p<.001) and 6 MWTD (0.415; p<.001) and positively correlated with E/e’ (0.352, p<.02) and LAVI (0.296; p<.05). By a multivariate regression analysis, FQRS (OR¼6.13; p<.001) and CFR (OR¼3.28; p<.001) were the only two independent predictors for decreased 6 MWTD in hypertensive patients. Importantly the 3 cutoff number of leads was found to be the best predictor of CFR < 2.0 in hypertensive patients. Conclusion: FQRS is frequent and an independent predictor of reduced exercise tolerance in hypertensive patients. More so, it is significantly associated with decreased CFR and left ventricular diastolic dysfunction. In light of these findings, fragmented QRS might be considered a simple marker for risk stratification of hypertensive patients.