The effect of infarct expansion (IE) on left ventricular function was studied in rats 9 days after transmural myocardial infarction produced by left coronary occlusion. The results showed that: Although the volume of infarcted myocardium were similar in IE group (N = 9

33.6+1.1%) and non-IE group (N = 14

34.4 + 2.1%

P >0.5)

the surface area of left ventricle (LV) occupied by infarcted tissue was larger in IE group than in non-IE group (49.0 + 1.1% vs 43.7+1.9%

P<0.0005).The infarcted wall thi ckness was also thinner in IE group (P<0.02). Obvious IE could only be seen in the LVs with more than 28% of myocardium infarcted

which showed that the infarct size (IS) is one of important determing factors of IE. But the degree of IE was not affected by IS (r = 0.284

P>0.1). The function indices of LV obtained during baseline or loading states

such as CI (332 + 14 in IE group vs 398 + 14 ml/min/kg in non-IE group

P<0.01)

-dp/dtmax (3211+220 vs 3879 + 201 mmHg/sec

P<0.05) and dp/dtmax (5722 + 415 vs 7392 + 460 mmHg/sec

P<0.05)

had significant difference between the two groups. In 29 infarcted rats

the significant correlations between the degree of IE and CI (r-- 0.561

P<0.002)

-dp/dtmax (r=-0.561

P<0.002)

and dp/dtmax (r=-0.534

P<0.005) were present. Thus

it is concluted that IE is an independent influence factor of infarcted LV function.