17 patients were treated by atrial (AAI) or atrial-triggered ventricular pacing (VAT). The atrial electrode was placed using a new endocardial screw-in technique. No complications occurred during a follow-up period of 3 months. Cardiac output at rest was measured in 12 patients before pacemaker implantation and was 3.571/min with VVI pacing at a heart rate (HR) of 70/min and 3.97 l/min (HR 75/min) with AAI or VAT pacing (p less than 0.001). Measurement of cardiac output was repeated in 7 patients with AV-block III degrees 10 weeks after pacemaker implant and the result was 4.40 l/min (HR 77/min) on VAT stimulation. During dynamic exercise in 5 patients, cardiac output under VAT pacing was 20% higher than with VVI pacing. This difference remained unchanged after 10 weeks. It is concluded that atrial electrodes can be placed reliably by the new technique. In contrast to VVI pacing, the hemodynamic benefits of atrial-triggered ventricular pacemakers appear to be long lasting.