Purpose: The purpose of this study was to evaluate the relation between serum markers of myocardial fibrosis and coronary flow reserve (CFR) using transthoracic Doppler echocardiography (TTE) in patients with arterial hypertension. Methods: In fifty-eight subjects (M:F= 31:27, mean age 57짹9 years) with chest pain and normal coronary angiogram, CFR was estimated with TTE and adenosine(140 關g/kg/min) and serum PIP (carboxy-terminal propeptide of procollagen type I), TGF-棺(trasforming growth factor-棺), MMP-3 (metalloproteinase 3) and TIMP-1(tissue inhibitor of metalloproteinase 1) were measured as serum markers of myocardial fibrosis. The subjects were divided into 3 groups: 19 hypertensives with CFR < 2.0 (group A, mean CFR=1.88짹0.43) 23 hypertensives with CFR ���2.0 (group B, mean CFR=2.90짹0.50) and 16 normotensives with CFR��� 2.0 (group C, mean CFR=3.09짹0.70). Patients with a history of acute myocardial infarction, regional wall motion abnormalities, wall thickness more than 12 mm of interventricular septum and posterior wall,left ventricular ejection fraction less than 55%, or primary valvular heart disease were excluded from this study. Results: 1.Baseline coronary flow velocity was 28.9짹17.0 cm/s in group A, 16.9짹5.5 cm/s in group B and 14.6짹4.1 cm/s in group C(0.005 versus group B and group C). 2. Serum PIP was 131.35짹31.76 關g/L in group A, 107.66짹26.04 關g/L in group B, and 90.10짹22.35 關g/L in group C (p<0.0001 versus group B and group C. 3. There were no significant differences in serum TGF-棺, MMP3 and TIMP1 levels among 3 groups. 4. Serum PIP in group C was closely related to CFR(r=0.67, p=0.0043). 5. A cutoff of 120 關g/L for PIP provided 59 % sensitivity and 74% specificity for predicting CFR<2.0 in hypertensives. Conclusion: This results show a relation between the severity of myocardial fibrosis and CFR in hypertension. Thus, the measurement of PIP may be useful for the elucidation of the mechanism causing impaired CFR in hypertensive patients with chest pain and normal coronary angiogram.