To study pathophysiological significance of Tl-201 lung uptake in coronary artery disease Tl-201 lung uptake was studied in 159 patients with chronic phase of myocardial infarction. Tl-201 lung uptake images were collected after rest Tl-201 myocardial imaging. Tl-201 lung uptake was estimated by comparing maximal lung counts with maximal myocardial counts (thallium lung heart ratio: LHR). Good correlation between LHR and mean pulmonary artery wedge pressure (mPw) and between LHR and left ventricular ejection fraction (EF) were obtained, (mPw = 2.7 +/- 10.5 LHR r = 0.52 n = 102, p less than 0.001, EF = 84.9-52.2 LHR r = -0.61 n = 159, p less than 0.001). It was noted that Tl-201 did not accumulate uniformly through the lung field and usually maximal Tl-201 lung uptake was noted at the basal zone of the right lung. Tl-201 lung uptake in the upper zone of the right lung increased in proportion to the hemodynamic deterioration. Interesting differences were noted between Tl-201 lung uptake in patients with chronic phase of myocardial infarction and that in patients with acute phase of myocardial infarction. The prognosis and clinical status of patients with markedly increased Tl-201 lung uptake (LHR greater than 0.8) in chronic phase were more excellent than the patients with similar Tl-201 lung uptake in acute phase. Hemodynamic parameters in patients with markedly increased Tl-201 lung uptake (LHR greater than or equal to 0.8) in chronic phase were significantly better than in those in acute phase.(ABSTRACT TRUNCATED AT 250 WORDS)