Similar to the effects of catalase, PC-specific overexpression of both the cytosolic and mitochondrial isoforms of SOD (SOD1 and SOD2) increased the incidence of cardiac arrhythmia and caused constriction of the heart tube (Figures S3A, S3B, S3D, S3E, and S3G–S3I). Here, CAT is linked to chronic obstructive pulmonary disease.