A candidate marker for ventricular remodeling after myocardial infarction (MI), syndecan-1 (Sdc1), has been shown to be upregulated in myocardial tissues. However, the clinical potential of this marker depends on the ability to obtain samples safely and noninvasively. Therefore, we investigated the expression of soluble Sdc1 in the serum of rats after MI. Anterior descending coronary arteries of Sprague-Dawley rats were ligated, and MI was confirmed by morphologic and physiologic methods. Rats that underwent surgery without ligation served as the control group. We analyzed the expression of Sdc1 mRNA by quantitative reverse-transcription polymerase chain reaction and that of Sdc1 protein by western blot in heart tissue from the MI border and compared it to the expression of soluble Sdc1 in serum. The myocardial levels of expression of Sdc1 mRNA and protein were very low in the sham group but increased significantly in the MI group (P<0.01). The expression of myocardial Sdc1 reached a peak at day 3 and declined gradually thereafter, although the levels at 14 days remained significantly higher than those in the sham group. The expression of soluble Sdc1 in the sera of the rats in the MI group followed a similar pattern and was linearly correlated with the expression of Sdc1 protein in the MI border zone (r=0.952, P<0.01). Soluble Sdc1 was also detected at low levels in normal rat serum. These results may facilitate additional exploration of the utility of serum Sdc1 as a biomarker for MI in humans.