1. CS-1170 was administered for the purpose of prophylaxis during cardiac catheterization in patients with heart disease, and its blood levels were measured. 2. The mean blood level (Moni-Trol I standard) after one intravenous shot of 20 mg/kg was 53.6 mcg/ml in catheterized children aged below 6 and 66.9 mcg/ml in catheterized children aged above 10 at 30 minutes, and 1.95 mcg/ml and 5.2 mcg/ml respectively at 6 hours. 3. The mean half life of the blood level was 1.09 hours in catheterized children aged below 6, 1.37 hours in catheterized children aged above 10, and 0.71 hours in infections children. 4. The urinary excretion seemed satisfactorily high although there was a great variation. 5. The clinical efficacy was 88.9%. 6. The bacteriological efficacy was 100% for E. coli, Klebsiella, Proteus mirabilis and Staphylococcus aureus and was 0% for Staphylococcus epidermidis. 7. Although GOT and GPT were elevated in one case as a side effect, they rapidly returned to normal after discontinuation of administration.