A simultaneous determination of four inorganic cations in cardioplegic solution was examined by indirect photometric ion chromatography (PIC). Cardioplegic solution was diluted 100-fold with 2.5mM copper sulfate aqueous solution, treated with SEP-PEK C18 and ACCELL PLUS QMA cartridges, and then injected into the chromatograph. Large amounts of sodium, potassium and magnesium and small amount of calcium were separated on a Zorbax SCX-300 column with 2.5mM copper sulfate solution as an eluent, and detected as negative absorption peaks by an ultraviolet (UV) photometric detector at 230 nm. Straight calibration curves for the cations were obtained from 0.05 to 1.5mM by using a peak height ratio method. The reproducibility of the data was good enough. When cardioplegic solution was diluted 4-fold with the eluent, the determination of calcium in sample solutions was sufficiently good, in spite of over-loadings of the other cations on column. The results obtained by the PIC method were more accurate than those of the autoanalyzer meth