To investigate the influence of selective beta 1-adrenergic blockade, in contrast to beta 1- and beta 2-adrenergic blockade, systemic and coronary hemodynamics were studied. Measurements were made at rest and during exercise in 23 patients with suspected coronary artery disease (CAD) before and after either metoprolol or propranolol, given in doses to provide comparable beta 1-receptor blockade. Quantitative coronary angiography was performed at rest. Using a randomized, double-blind protocol, either beta 1 and beta 2 blockade was produced by propranolol (0.1 mg/kg intravenously), or selective beta 1 blockade was produced by metoprolol (0.15 mg/kg intravenously). As expected, at these doses both drugs produced a comparable decrease in heart rate at rest and during exercise, averaging 9% and 14% after propranolol and 10% and 16% after metoprolol. Exercise duration to ischemia was prolonged in most patients with severe CAD after either propranolol (5 of 7) or metoprolol (6 of 10) treatment. The effects of these 2 beta-blocking drugs on systemic hemodynamic values at rest and during exercise were similar. Additionally, coronary sinus flow was usually unchanged by both drugs at rest (-5% after propranolol and -4% after metoprolol, differences not significant) and decreased a similar amount during exercise (-15% after propranolol and -9% after metoprolol, both p less than 0.05). Coronary resistance did not change significantly with either drug (0% after propranolol and 3% after metoprolol), and during exercise (11% after propranolol and 3% after metoprolol), suggesting that decreases in flow were secondary to reduced demand. Furthermore, neither drug produced detectable changes in coronary artery size.(ABSTRACT TRUNCATED AT 250 WORDS)