Phosphoinositide-3 kinases (PI3Ks) are a family of evolutionary conserved lipid kinases that mediate many cellular responses in both physiologic and pathophysiologic states. Class I PI3K can be activated by either receptor tyrosine kinase (RTK)/cytokine receptor activation (class I_A) or G-protein-coupled receptors (GPCR) (class I_B). Once activated PI3Ks generate phosphatidylinositols (PtdIns) (3,4,5)P₃ leading to the recruitment and activation of Akt/protein kinase B (PKB), PDK1 and monomeric G-proteins (e.g. Rac-GTPases), which then activate a range of downstream targets including glycogen synthase kinase-3β (GSK-3β), mammalian target of rapamycin (mTOR), p70S6 kinase, endothelial nitric oxide synthase (eNOS) and several anti-apoptotic effectors. Class I_A (PI3Kα, β and δ) and class I_B (PI3Kγ) PI3Ks mediate distinct phenotypes in the heart and under negative control by the 3′-lipid phosphatase, phosphatase and tensin homolog on chromosome ten (PTEN) which dephosphorylate PtdIns(3,4,5)P₃ into PtdIns(4,5)P₂. PI3Kα, γ and PTEN are expressed in cardiomyocytes, fibroblasts, endothelial cells and vascular smooth muscle cells where they modulate cell survival/apoptosis, hypertrophy, contractility, metabolism and mechanotransduction. Several transgenic and knockout models support a fundamental role of PI3K/PTEN signaling in the regulation of myocardial contractility and hypertrophy. Consequently the PI3K/PTEN signaling pathways are involved in a wide variety of diseases including cardiac hypertrophy, heart failure, preconditioning and hypertension. In this review, we discuss the biochemistry and molecular biology of PI3K (class I isoforms) and PTEN and their critical role in cardiovascular physiology and diseases.