[en] Programmable pacemakers (PPM) can be programmed to sense, stimulate, or inhibit atrial (A) and/or ventricular (V) electrical activity, and include variable A-V delays and other options. Selecting the optimum combination of settings for an individual patient can be a formidable task in the absence of noninvasive, objective, quantifiable measures of cardiac function. The authors attempt to determine whether the MUGA study could be adapted to such a task. MUGA studies were performed on 13 patients (pts) with PPM who had varying degrees of A-V block, during various settings of the PPM's. Studies were carried out 5-10 min. after pacing mode and A-V delay were changed, with the pt resting and supine. All 5 MUGA studies were carried out after a single injection of Tc-99m labeled autologous red blood cells. The results show that the VDD mode brings about a higher left ventricular ejection fraction (LVEF) and cardiac output (CO) than the DVI mode, and that either of these dual-chamber pacing modes produces a higher LVEF and CO than single-chamber pacing (VVI). Furthermore, a longer A-V delay was shown to improve LVEF and CO in patients with initially low LVEF. The MUGA study is simple, noninvasive, objective, and quantifiable, and can easily be repeated several times following a single injection. It can be used to ''fine tune'' programmable pacemakers for optimum hemodynamic performance