To analyze the effects of acute elevations in arterial blood pressure on pulmonary blood volume (PBV) and left ventricular function, 21 outpatients with congestive cardiomyopathies and stable condition and eight normal control subjects were studied using equilibrium radionuclide angiography during the infusion of phenylephrine. The myopathy patients were subdivided into seven patients who developed rales during phenylephrine infusion and 14 who did not. All of the myopathy subjects had reduced ejection fractions and enlarged end-diastolic volumes at rest. With phenylephrine, the patients who developed rales (Group 1) and those who did not (Group 2) had similar changes in left ventricular parameters (ie, ejection fraction declined and end-diastolic volume increased). With phenylephrine, however, the patients with rales had marked increases in radionuclide estimates of PBV (48.2 +/- 1.2 to 71.2 +/- 4.1 units, P less than .01, a mean increase of 48%), while in the subjects without rales, PBV increased from 48 +/- 11 to 54.6 +/- 2.2 (P less than .05, a mean increase of only 14%). Normal individuals (Group 3) had a qualitatively similar response to phenylephrine as did the myopathy patients (a decline in ejection fraction and an increase in end-diastolic volume), with no significant change in PBV. Noninvasive phenylephrine radionuclide imaging may help characterize patients with varying forms of congestive cardiomyopathies, direct appropriate therapy, and help explain the pathophysiology of clinical findings.