1. In patients with dilated cardiomyopathy, abnormal myocardial blood flow may contribute to poor myocardial function.

2. The aim of this study was to investigate the possible contribution of abnormal myocardial blood flow to the limitation of exercise capacity in patients with dilated cardiomyopathy.

3. Coronary flow reserve was assessed in 16 patients with dilated cardiomyopathy and 9 matched normal control individuals. All participants had angiographically normal coronary arteries. At rest and after dipyridamole infusion (0.56 mg/kg intravenously), peak systolic and diastolic coronary flow velocities were measured in the proximal left anterior descending coronary artery using transoesophageal pulsed Doppler echocardiography, guided by colour flow imaging. Coronary flow reserve was calculated as the ratio of hyperaemic to basal diastolic and systolic peak coronary flow reserve.

4. Baseline diastolic and systolic coronary flow velocities were significantly higher in patients (50 ± 6 and 30 ± 4 cm/s respectively) compared with control individuals (37 ± 3 and 20 ± 1 cm/s respectively) (mean ± S.E.M.) (P < 0.05). Diastolic and systolic peak coronary flow reserve were significantly lower in patients (1.60 ± 0.14 and 1.40 ± 0.09 respectively) compared with control individuals (2.89 ± 0.15 and 2.17 ± 0.17 respectively) (P < 0.001). Although peak Vo2 and exercise time were significantly lower in patients compared with control individuals, coronary flow reserve did not correlate to exercise capacity in patients with dilated cardiomyopathy.

5. These results confirm the abnormalities of coronary flow reserve previously observed in patients with dilated cardiomyopathy, but suggest that such abnormalities do not contribute to the limitation of exercise capacity in these patients.

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