We have recently demonstrated that the activity of the inhibitory guanine nucleotide-binding regulatory protein Gi is increased in the hearts of patients with idiopathic dilated cardiomyopathy. We determined whether altered Gi protein levels in the failing human heart correlate with changes in steady state levels of the mRNA encoding one of the alpha Gi peptides. cDNAs encoding alpha Gs, alpha Go, and three subspecies of alpha Gi were used as hybridization probes to quantify steady state levels of mRNA encoding these alpha G peptides in failing and non-failing human heart. The lengths of the mRNAs that encode each alpha G peptide were the same in non-failing and failing hearts. Steady state levels of mRNA encoding both alpha Gi-3 and alpha Gs were significantly increased in the failing hearts when compared to non-failing hearts. By contrast, there was no significant change in the levels of mRNA encoding alpha Go or of rRNA. The relative abundance of the mRNA encoding each of the subspecies of alpha Gi was different in the human heart; alpha Gi-3 mRNA was abundant, alpha Gi-2 was barely detectable, and we were not able to detect alpha Gi-1 utilizing our hybridization conditions. These results suggest that alterations at the level of transcription as well as post-translational modifications can affect the activities of transmembrane signaling proteins in chronic congestive heart failure.