The strong association between severe coronary stenosis and collateral growth continues to be a paradigm in this field of investigation. The present study was based on the hypothesis that angiogenic growth factors are produced by ischemic cardiac tissue, are diffusible and more concentrated in pericardial fluid, and accelerate the growth of vascular smooth muscle cells (VSMC). Pericardial fluid from 17 patients with stable or unstable angina or acute myocardial infarction (group A) and from 10 patients with nonischemic heart disease (group B) were collected at the time of open heart surgery. Cultured human aortic VSMC were plated at the third passage at a density of 5x10(3)/100 microl and allowed to attach for 24 h. The 3-day growth assay was preceded by 72 h of growth arrest with 0.4% fetal calf serum (FCS). Growth was restarted by the addition of 90 microl of medium containing 0.4% FCS, and 1O microl of each pericardial fluid. Cell counts on triplicate wells were performed using a dimethylthiazol (MTT) method on days 0 and 3. The effect of pericardial fluid on the growth of VSMC was evaluated as a ratio (R) of cell numbers on day 3 to those on day 0. The concentration of basic fibroblast growth factor (bFGF) in pericardial fluid was measured by an enzyme-linked immunosorbent assay. The concentration of bFGF in pericardial fluid of group A was 633+/-127 pg/ml, and significantly (p=0.003) higher than that of group B (86+/-23 pg/ml). R in group A was 2.29+/-0.18 and significantly (p=0.019) higher than that in group B (1.68+/-0.11). The level of bFGF positively correlated with R (p=0.009). These findings indicate that pericardial fluid from patients with ischemic heart disease contains some substances that mediate collateral development, and bFGF might be one of them.