BACKGROUND Cardiac myocyte hypertrophy results from clinical conditions that include hypertension and valvular heart disease, and can result in heart failure. This study aimed to investigate the expression and role of the long noncoding RNA FTX (lnc-FTX), an X-inactive-specific transcript (XIST) regulator transcribed from the X chromosome, in hypertrophy of neonatal mouse cardiac myocytes induced by angiotensin II (Ang II) in vitro. MATERIAL AND METHODS Cardiac myocytes were isolated from neonatal mice and cultured with and without Ang II. Immunofluorescence, with localization of an antibody to alpha-smooth muscle actin (alpha-SMA), was used to identify the neonatal mouse cardiac myocytes. Quantitative real-time polymerase chain reaction (qRT-PCR) measured gene expression levels. The cell counting kit-8 (CCK-8) assay was used to determine cell viability, and Western blot measured protein expression. StarBase v2.0 bioinformatics software was used for target gene prediction and was confirmed with the luciferase reporter assay. RESULTS The expression of lnc-FTX was reduced in mouse cardiac myocytes treated with Ang II. Overexpression of lnc-FTX reduced cell apoptosis, cardiomyocyte contractility, and the expression of c-Jun, A-type natriuretic peptide (ANP), and B-type natriuretic peptide (BNP) induced by Ang II. The target of lnc-FTX was micro-RNA 22 (miRNA-22). The mechanism of action of lnc-FTX in neonatal mouse cardiac myocytes was through suppression of the PI3K/Akt signaling pathway by promoting the release of PTEN by sponging miRNA-22. CONCLUSIONS The expression of lnc-FTX was associated with reduced hypertrophy of neonatal mouse cardiac myocytes and regulated the PTEN/PI3K/Akt signaling pathway by sponging miRNA-22.