Accumulated laboratory and clinical information indicates that the unhurried and meticulous correction of many intracardiac defects will require the benefits of total cardiac by-pass. The addition of controlled cardiac arrest to the technique of total cardiac by-pass has certain positive advantages, which have been demonstrated by Melrose,1 Lam,2 and Young.3 The most important of these are the absence of coronary blood flow and the quiet, relaxed heart. The duration of time for which a heart can be arrested safely during total cardiac by-pass is as yet undetermined. It is evident from studies previously reported4,5 that at least 20 minutes of controlled asystole is well tolerated by canine and human hearts. The purpose of this study is to discuss induced asystole in dogs extended to 60 minutes during total cardiac by-pass. Extracorporeal circulation was maintained with a finger pump and a rotating stainless steel disk oxygenator6