To evaluate the effects of warm continuous versus cold intermittent blood cardioplegia on coronary blood flow patterns after prolonged cardioplegic arrest, nine pigs underwent cardiopulmonary bypass with 210 minutes of aortic cross-clamping. Antegrade blood cardioplegia was administered either cold intermittent (n = 4) or warm continuous (n = 5). During the first 30 minutes of reperfusion, there was decreased coronary blood flow with higher coronary vascular resistance in the cold group (mean +/- standard error; warm vs. cold: 30 min: flow: left anterior descending artery (LAD): 66 +/- 6 vs 36 +/- 4 ml/min, right coronary artery (RCA): 88 +/- 2 vs 61 +/- 4, p < 0.05, resistance: LAD: 33 +/- 3 vs 69 +/- 5 dyn.s.cm-5 x 10(3), RCA: 41 +/- 3 vs 58 +/- 8, p < 0.05). After one hour of reperfusion there were no differences between groups. Arterio-venous oxygen difference was higher in the cold group after 15 min (3.1 +/- 0.5 vs 4.8 +/- 0.3 ml O2/100 ml, p < 0.05) and 30 min (4.2 +/- 0.5 vs 6.2 +/- 0.7, p < 0.05) with equal values after 1 hour. During reperfusion there is reduced myocardial blood flow after cold intermittent blood cardioplegia. This may reflect superior myocardial protection with warm continuous cardioplegia.