A chemically stable prostacyclin analogue (PGI2-A, carbacyclin, OP-41483) was evaluated as an adjunct to potassium cardioplegia in infants (n = 13) and children (n = 32), in whom the current potassium cardioplegia may be limited in its effects. PGI2-A was added in a dose of 300 micrograms/L to the potassium cardioplegic solution. Postoperatively, peak levels of the myocardial-specific isoenzyme of creatine kinase (MB-CK) were compared for the PGI2 group and a control group (n = 65). In patients 1 year of age or older (n = 32 and 49 for the PGI2 and control groups, respectively), the MB-CK level was significantly lower in the PGI2 group only when compared between the subgroups with an aortic cross-clamp time of 120 minutes or more (n = 9 and 10; MB-CK level, 35.2 +/- 15.6 vs 68.3 +/- 32.4 IU/L;p less than 0.05). In patients less than 1 year of age, in whom aortic cross-clamp times were generally less than 120 minutes, the MB-CK level was also lower in the PGI2-A group than in the control group (n = 13 and 16; MB-CK level, 33.6 +/- 14.3 vs 61.6 +/- 36.3 IU/L;p less than 0.05). Infants less than 6 months of age (n = 18) underwent ultrastructural assessment of left ventricular myocardial biopsy specimens, and the PGI2-A group showed better results in mitochondrial and intracellular edema scores. This clinical trial showed beneficial effects of PGI2-A used with crystalloid potassium cardioplegia in infants and children.