A new method for carrying out surgical procedures inside the cavities of the heart was described in our preliminary report.1 Only the method for carrying out these intracardial surgical procedures was discussed. Since the method is new, we shall describe it again, and, in addition, discuss some of the effects on the heart and the two circulations subsequent to carrying out certain of these procedures on the mitral valves. METHOD We have approached the problem of intracardiac surgery from the point of view of the surgeon. Our aim was to develop a practical method for carrying out surgical procedures inside the cavities of the human heart. We were not satisfied, therefore, with any method that would be useful in the experimental laboratory but that was clearly not applicable in the operating room. This distinction is important. From the beginning of this experimental work, we believed that such operations, if