Stimulation of left ventricular stretch receptors has been proposed as a possible mechanism for the occurrence of cardiac pain. Changes in left ventricular volume were continuously assessed in 12 patients during 11 spontaneous (two painful) and 12 ergometrine-induced (nine painful) ischemic attacks with a precordial scintillation probe and blood pool labeling with technetium-99m. In all ischemic episodes, spontaneous or induced, painful or painless, severe dilatation of the left ventricle was consistently observed. These changes always preceded the onset of ST segment shifts and occurred long before pain, when present. The maximum increase in end-diastolic volume was slightly greater in painful than in painless episodes, 38 +/- 8.0% versus 28 +/- 12.4%, but no significant difference was observed in the rate of volume change or in the maximum increase of end-systolic volume (133 +/- 50% and 110 +/- 27.3%), stroke volume (-28 +/- 15% and -25 +/- 12.4%), or ejection fraction (-32 +/- 8.7% and -26 +/- 6.0%). Although the maximum end-diastolic volume achieved is greater in painful episodes, this effect cannot be separated from that of duration, and, furthermore, there was no significant difference in end-diastolic volume at the moment chest pain began. Thus, in patients with angina at rest, transient asymptomatic ST segment shifts are consistently associated with large changes in left ventricular volume, similar to those observed during painful episodes. The rate and extent of acute left ventricular dilatation do not appear to be factors directly causing anginal pain.