Prior studies of cold retrograde cardioplegia have demonstrated the existence of regional deficits in perfusate delivery. To address the hypothesis that these deficits persist with the use of warm perfusate, cardioplegic arrest was induced in 7 swine hearts with retrograde warm blood cardioplegia. Regional perfusion was assessed with the simultaneous infusion of colored 10-microns microspheres. The percentage microsphere recovery (regional microsphere count/total number of microspheres counted x 100) was greatest in the anterior (43% +/- 4%) and lateral (35% +/- 6%) left ventricle. The microsphere recoveries in the posterior left ventricle (7% +/- 1%) and anterior septum (14% +/- 4%) were intermediate, and were statistically lower than those in the anterior left ventricle (p < 0.01). The lateral right ventricle (0.6% +/- 0.2%) and the posterior septum (1.4% +/- 0.9%) exhibited minimal perfusion versus that in the anterior left ventricle (p < 0.01). Less than 1% of the infused microspheres were recovered in the aortic root; 67% were recovered in the right ventricle and are presumed to have bypassed the microcirculation as nonnutritive flow. These data demonstrate that cold retrograde perfusion patterns persist during retrograde warm blood cardioplegia. Limited perfusion of the right ventricle and the posterior septum as well as a large nonnutritive flow were also noted. These perfusion deficits in metabolically active arrested hearts may limit myopreservation at low cardioplegia flow rates.