Multiple pathways can regulate cardiomyocyte growth, acting through a complex network of intracellular signalling cascades. Agonists for α-adrenergic, angiotensin, and endothelin receptors couple to phospholipase C (PLC) and calcium influx channels (CC) by way of G-proteins (Gα and Gγ). Activation of PLC results in the generation of two second messengers, inositol triphosphate (IP3) and diacylglycerol (DAG). IP3 causes the release of calcium from intracellular stores, and DAG activates protein kinase C (PKC). Changes in intracellular calcium stores can activate calcium-calmodulin-dependent kinases (CaCMK), as well as calcineurin, which affect gene expression in multiple ways. The modulation of other membrane transporters (such as the Na+-H+ exchanger which regulates cellular pH) and the activation of mitogen-activated protein kinase (MAPK) cascades are also involved. Histone deacetylase complexes (HDACs) are emerging as important negative regulators of genes involved in cardiac hypertrophy. Cytokines and peptide growth factors can be elaborated by various cells within the heart and may act in an autocrine or paracrine manner, generally via tyrosine kinase (TK) receptors that are coupled to downstream protein kinase signalling cascades cascade. Mechanical forces can also affect hypertrophy through several pathways, including direct effects at the level of the sarcomere, alterations in matrix-integrin interactions and the autocrine action of released agonists such as angiotensin. Both nitric oxide and reactive oxygen species are capable of modulating distinct signalling pathways within the cell, either in a negative or positive fashion depending upon circumstances. The net effects of such intracellular signalling include myocyte hypertrophy, changes in contractile function and altered cell viability. (Adapted from Mann DL, Pathophysiology of Heart Failure. In Bonow RO, Mann DL, Zipes DP, Libby P [eds]: Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine, 9th ed, pp ????, 2010).