Sudden death and arrhythmias are significant problems in patients with various types of repaired congenital heart disease and have been associated with increasing time after and older age at surgery. Arrhythmias have been mapped clinically to areas of surgical scars in some patients, leading to the hypothesis that scar morphology changes with age. This study compared the morphology and histology of right ventriculotomy scars or right atriotomy scars in newborn (2 to 3 weeks), young (5 to 8 weeks), and older (> or = 6 months) dogs at postmortem examination 5 months postoperatively. Atriotomy lengths increased significantly compared with the initial incision in the newborn (6.0 mm +/- 0.1 to 15.2 mm +/- 5.8; p < 0.05) and young (6.8 mm +/- 0.9 to 19.6 mm +/- 4.8; p < 0.01) groups but were similar in the older group (35.5 mm +/- 11.7 to 27.0 mm +/- 2.5). Ventriculotomy scars grew 110 +/- 69% in the newborn group and 126 +/- 71% in the young group but shrank 31 +/- 6% of the original length in the older group (young vs older; p < 0.05). This increase in the atriotomy and ventriculotomy scars in the young group and the decrease in the older group resulted in scars of similar length; only those scars in the newborn group remained significantly shorter than scars in the older group (p < 0.05). Atriotomy and ventriculotomy scars in the older group had more bone or cartilage (p < 0.05) but less dystrophic calcification (p < 0.05) than those scars in the younger groups.(ABSTRACT TRUNCATED AT 250 WORDS)