Quantification of mRNAs from extremely small human samples remains a challenge. Requiring minimal amounts of tissue and no post-reaction manipulation, real-time reverse transcriptase-polymerase chain reaction (RT-PCR) is an attractive method to quantitatively assess the expression of rare mRNAs. We evaluated the applicability of the technique on RNA extracted from human endomyocardial biopsies and isolated cardiomyocytes, and compared the technique to the RT-competitive PCR approach. Primers and probes were designed to amplify the three subtypes of human β -adrenoceptors (β 1-,β 2- and β 3 AR), as well as reference genes such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Hypoxanthine-guanine phosphoribosyltransferase (HPRT), and the oncogene ABL by real-time RT-PCR. Specific primers and a deleted competitor were synthetized to compare the quantitation of the β 3 AR mRNA expression by RT-competitive PCR. We validated the technique on human cardiomyocytes either freshly isolated or selectively excised from fixed sections of human myocardium by Laser Capture Microdissection. The standard curves obtained for the cDNA's analysed showed mean slopes comprised between −3.3 and −3.7. Inter- and intra-assay variablility of gene quantitation was reflected by mean values of the variance coefficients of Ct of 4.84±1.13% and 2.73±0.39% or 3.32±1.03% and 2.21±0.24% (corresponding to percent variances of copy numbers of 83.07±12.72% and 34.45±9.03% or 47.40±8.59% and 23.83±3.16%) for human β 3 AR and GAPDH genes, respectively. The expression of GAPDH, HPRT and ABL mRNA was characterized by a very low dispersion of individual values across cardiac pathologies, suggesting that these genes may be used as reference genes in quantitative PCR studies. Finally, we applied the technique to detect rare mRNAs, such as β -AR mRNAs, from small human endomyocardial biopsies and even isolated cardiomyocytes. Real-time RT-PCR is appropriate to quantitate rare messenger RNAs, including in extremely small human tissue samples. This method appears very promising for futures studies of gene expression in several pathophysiological conditions, including heart failure.