Nine adult mongrel dogs were subjected to cardiopulmonary bypass and both right and left atria were surgically isolated, exclusive of the sinoatrial (SA) node, crista terminalis, and interatrial septum. Thus, the SA node remained in continuity with the ventricles despite biatrial isolation. Moreover, of the right and left SA node arteries, the predominant one (right in 7 dogs, left in 2 dogs) was spared. Postoperatively, normal SA node function was preserved in 8 out of 9 dogs, with no difference in sinus rhythm cycle length (preop: 446 +/- 25, postop: 434 +/- 22 sec, p = NS) or sinus node recovery time (preop: 488 +/- 28, postop: 487 +/- 32 msec, p = NS). Simulated supraventricular tachycardia was confined in the isolated right or left atria did not affect sinus rhythm in the remainder of the heart. One out of 9 dogs developed junctional rhythm postoperatively, indicating exclusion of the SA node or a fast atrial pacemaker. In the 8 dogs with postoperative sinus rhythm, the spared SA node artery was occluded at the end of each study. All dogs developed rhythm deterioration including sinus rhythm slowing with prolonged sinus node recovery time (4 dogs), sinus bradyarrhythmia (2 dogs) and atrioventricular nodal rhythm (2 dogs). Thus, biatrial isolation is feasible for the treatment of supraventricular tachycardia, but it is essential to preserve SA node blood supply in order to maintain normal sinus rhythm in the remainder of the heart.