The detection of cardiac troponins in peripheral blood as protein markers of myocardial infarction is a new diagnostic tool in the diagnosis of cardiac disease. In order to increase the sensitivity and specificity of this diagnostic approach, a reverse transcription polymerase chain reaction assay has been developed to detect the mRNA encoding cardiac troponin I from myocardial cells hypothetically released from damaged cardiac tissue. The detection is specific for cardiac troponin I mRNA, with no amplification of homologous sequences of other troponin I isoforms, i.e., troponin I from skeletal muscle cells. However, a strong amplification signal for cardiac troponin I mRNA was detected in samples of peripheral blood from healthy human volunteers. In patients with acute myocardial infarction or angina pectoris, the cardiac troponin I mRNA levels were not increased over background levels. In conclusion, a reverse transcription polymerase chain reaction approach based on the amplification of cardiac troponin I mRNA is not feasible in the diagnosis of cardiac diseases.