Muscarinic receptors are G-protein coupled receptors, existing in 5 subtypes. These subtypes differ in their effects on second messenger systems. While the odd-numbered subtypes activate phospholipase CR, and then they increase the production of inositoltrisphosphate and diacylglycerol, even-numbered subtypes inhibit adenylylcyclase. The expression of individual subtypes is highly tissue specific. Heart is obviously thought as M2 specific tissue. This article reviews the evidence of inositol metabolism stimulation in the heart, i.e. the interaction with effector system other than adenylylcyclase. Possibilities of odd-numbered subtypes expression in the heart are also discussed.

        Key words: muskarinic receptors, heart atria, heart ventricles, phospholipase C, phosphatidilinositol