Abstract: Objective To explore the stability of internal controls in human cardiac muscle by real-time RT-PCR during early postmortem interval（PMI） in order to find the most stable marker. Methods Ten individuals with similar environmental conditions （the average store temperature： 25 ℃） and different PMI ranging from 4.3 to 22.3 h were selected. Total RNA was extracted from each sample and six commonly internal controls were used including β-actin, GAPDH, B2M, U6, 18S rRNA and HSA-miR-1, and the expression was detected in cardiac muscle by real-time RT-PCR. The expression stability of internal controls was evaluated using genorm^PLUS software during early PMI. The internal control with the most stability was selected. The relationship between the most stable marker and its expression level affected by some other parameters such as age, gender and cause of death was also analyzed. Results The U6 showed the most stable expression during early PMI in cardiac muscle, and its expression level was not affected by those parameters including age, gender and cause of death（P>0.05）. Conclusion U6 may be a valuable internal control for the study of relationship between PMI determination and degradation of nucleic acid in human cardiac muscle by real-time RT-PCR.

Key words: forensic pathology, reverse transcriptase polymerase chain reaction, myocardium, internal control, postmortem interval