To investigate the relationship between the heart-lung ratio (HLR) assessed with exercise 99TcmN-NOET myocardial perfusion imaging and coronary artery disease (CAD)

10 normal volunteers (7 male and 3 female

aged 40.0±5.8 years)

and 40 suspected CAD patients (21 male and 19 female

aged 55.2±8.5 years) underwent exercise (30 min)-delayed (2 and 4 h postinjection) 99TcmN-NOETgated myocardial perfusion imaging

and the HLR at different time was calculated. 13 patients among them took the coronary angiography in two months. According to the exercise heart-lung ratio (EXHLR)

50 subjects were divided into two groups. G1 (n=36

EXHLR≥2) included 10 normal volunteers

5 patients with normal coronary arteries

and the rest 21 patients had no relevant symptom and cardiac event in the follow-up period of 4 to 12 months. The image was normal in all of the subjects in G1. In G2 (n=14

EXHLR<2)

8 patients had significant CAD diagnosed by coronary angiography (≥50% luminal stenosis)

4 of the rest six patients had angina followed with typical ECG changes during the follow-up period. The HLR was of significant difference between the two groups at different time. In G2

nine patients had normal imaging results

of whom four CAD patients were verified by coronary angiography (stenosis 50%—70%)

while other five patients had redistribusion or fixed defect. The HLR of the 99TcmN-NOET may be useful as a diagnostic index in CAD because it is more sensitive than myocardial perfusion imaging.