The relation between perfusion of the infarct-related artery and changes in left ventricular volume and function during the month after a first myocardial infarction was examined in 40 patients who did not receive thrombolytic therapy. Infarct artery perfusion was documented at predischarge coronary angiography, and left ventricular volume was measured by nongeometric analysis of radionuclide angiograms performed within 48 hours of infarction and at 1 month. Left ventricular dilation (greater than or equal to 20% increase in volume) developed in 16 patients, whereas 5 patients had a decrease in left ventricular volume of greater than or equal to 20% by 1 month. Left ventricular dilation occurred in all 14 patients without perfusion of the infarct-related artery, compared with only 2 of 26 patients with perfusion of this artery due to subtotal occlusion or collateral vessels. All five patients whose left ventricular volume decreased by greater than or equal to 20% had a perfused infarct artery. Multiple linear regression analysis confirmed that the degree of perfusion of the infarct artery (partial r = 0.58, p = 0.001) was a more important predictor of volume change than was infarct size measured by peak creatine kinase (partial r = 0.30, p = 0.009) or QRS score (partial r = 0.20, p = 0.087). Left ventricular ejection fraction decreased from 0.38 +/- 0.10 to 0.30 +/- 0.16 (p = 0.05) in 11 patients with an anterior infarct and ventricular dilation; it increased from 0.45 +/- 0.10 to 0.62 +/- 0.07 (p = 0.02) in the 5 patients with a greater than or equal to 20% decrease in volume.(ABSTRACT TRUNCATED AT 250 WORDS)