Based on data obtained from a model of experimental heart failure in rats, which showed a ROCK-mediated inotropic response to M2R activation only in failing hearts [30] and a RhoA/ROCK-mediated, carbachol-induced inotropy in neonatal rat hearts upon M2R activation [40], we propose that the carbachol-induced RhoA/ROCK-mediated responses are elicited by this receptor subtype. This evidence concerns the gene RHOA and heart failure.