Peripheral vasodilation is commonly seen during and after warm heart operations and can become of clinical concern when it requires vasopressors because some of these drugs adversely affect coronary artery bypass graft flows. As hemodilution lowers systemic vascular resistance, we assessed whether peripheral vasodilation could be limited by a drastic reduction of the volume of infused cardioplegia. Fifty patients underwent isolated coronary artery bypass grafting procedures using normothermic (35 ° to 37 °C) bypass and normothermic continuous retrograde blood cardioplegia. They were divided into two equal groups: in group 1, blood was diluted 4:1 with hyperkalemic crystalloid cardioplegia, whereas in group 2, the cardioplegic "solution" was limited to the sole arresting agents that were concentrated in a small volume (16 mEq potassium chloride and 3 mEq magnesium chloride in a 20-mL ampoule). This "mini-cardioplegia" was continuously added to arterial blood so as to keep the heart arrested. The average volume of cardioplegia per patient was 1,000 mL in group 1 and 58 mL in group 2 (p < 0.0001). The mini-cardioplegia technique resulted in a reduced incidence of perioperative systemic vasodilation: group 2 patients required significantly less vasopressors (p < 0.05) and less volume loading, as reflected by significantly lower right atrial and pulmonary capillary wedge pressures (p < 0.05 and p < 0.03 at 12 hours postoperatively, respectively), compared with group 1 patients who received traditional high-volume cardioplegia. There were no differences between the two groups with respect to myocardial recovery, as assessed by standard clinical and hemodynamic end points. We conclude that a drastic reduction of the cardioplegic load, as afforded by the minicardioplegia technique, offers a simple and effective means of decreasing the incidence of systemic vasodilation occurring with warm heart operations without compromising myocardial protection provided by the normothermic approach. © 1993.