['Peroxisome proliferator-activated receptors (PPAR) alpha and beta/delta are essential transcriptional regulators of fatty acid oxidation in the heart. However, little is known about the roles of PPARgamma in the heart. The present study is to investigate in vivo role(s) of PPARgamma in the heart.', 'A Cre-loxP mediated cardiomyocyte-restricted PPARgamma knockout line was investigated. In these mice, exon 1 and 2 of PPARgamma were targeted to eliminate PPARgamma from cardiomyocytes.', 'PPARgamma null mice exhibited pathological changes around 3 months of age, featuring progressive cardiac hypertrophy with mitochondrial oxidative damage. Most mice died from dilated cardiomyopathy. Cardiac expression of Sod2 (encoding manganese superoxide dismutase; MnSOD), a mitochondrial antioxidant enzyme was downregulated both in transcript and protein levels in cardiac samples in PPARgamma knockout mice independent of pathological changes. Promoter analyses revealed that Sod2 is a target gene of PPARgamma. Consequently, myocardial superoxide content in PPARgamma knockout mice was increased, leading to extensive oxidative damage. Treatment with a SOD mimetic compound, MnTBAP, prevented superoxide-induced cardiac pathological changes in PPARgamma knockout mice.'] Is cardiac peroxisome proliferator-activated receptor gamma essential in protecting cardiomyocytes from oxidative damage?