The most serious and fatal operative complications of the closed heart surgical procedures are massive hemorrhage from an accidental left atrial tear unexpectedly. In these cases, had been equipped for elecktlically induced ventricular fibrillation, the blood loss might have been mininal and facilitated exposure to permit rapid suturing of the defect, so I would like to emphasize to the usefulness of induced vontricular fibrillation in the control of massive hemorrhage from the heart. So I had been carried on laboratory studies to induced ventricular fibrillation in normothermic dogs and obtained the following results. 1) Continuing the ventricular fibrillation for over 5 minutes duration, there were no surviveddogs, but all survived to the cirrulatory arrest within 4 minutes, three of the 4 dogs died but only I dog stayed alive between 4 to 5 minutes. It has been showed that in dog the safe length of circulatory arrest inducing ventricular fibrillation under normothermic conditions is 4 minutes. 2) Incising left atrium, the mean blood loss was 120ml per minute, equal to 15ml prokilogramm per minute. Inducing ventricular fibrillation soon after atriotomy, the mean blood loss was 80ml, equal to 12ml prolkilogramm per minut. The mcan blood loss was 50ml in atriotomy under induced ventricular fibrillation, equal to 4ml prokilogramm per minut, it was effective in reducing blood loss compared with the former. 3) Blood pressure almost dropped to Zero under ventricular fibrillation but there was not able to provide a dry operative field in the results of persistent venous return secondary to siphonage effect. Induced ventricular fibrillation definitly facilitates the intracardiac procedures and prevent air embolism from the removal of loose intracardiac thrombi.