Studies of controlled reperfusion after ischemia. XX. Reperfusate composition: detrimental effects of initial asanguineous cardioplegic washout after acute coronary occlusion. This study tests whether initial asanguineous washout of potentially toxic substances that accumulate during ischemia improves recovery produced by blood cardioplegic reperfusion and evaluates the role of plasma versus whole blood cardioplegia. METHODS: Twenty-four dogs underwent 2 hours of occlusion of the left anterior descending coronary artery and 20 minutes of blood cardioplegic reperfusion on total vented bypass. In 13 dogs, a 5-minute infusion of either a crystalloid (n = 7) or plasma (n = 6) cardioplegic solution (containing the same pH, calcium potassium, and osmolarity as blood cardioplegia) was given immediately before reoxygenation with blood cardioplegia. Regional oxygen uptake and coronary vascular resistance were measured during controlled reperfusion, and segmental shortening (ultrasonic crystals), tissue water content, and histochemical damage (triphenyltetrazolium chloride stain) were assessed 1 hour after bypass was discontinued. RESULTS: Asanguineous cardioplegic washout before reoxygenation with blood cardioplegic solution resulted in a progressive (+42%) increase in coronary vascular resistances (from 123 to 176 units, p less than 0.05) and low oxygen utilization during 20 minutes of blood cardioplegic reperfusion (29 ml/100 gm, p less than 0.05); coronary vascular resistance remained low throughout blood cardioplegic reperfusion without washout (from 109 to 98 units), and oxygen utilization was 54 ml/100 gm (p less than 0.05). Neither plasma nor crystalloid washout restored substantial regional systolic shortening (3% systolic shortening versus 73% systolic shortening with blood cardioplegia), and asanguineous washout caused more myocardial edema (81.1% +/- 80.9% versus 79.5% water content, p less than 0.05) and produced extensive transmural triphenyltetrazolium chloride damage (48% +/- 41% versus 8% nonstaining in area at risk, p less than 0.05) than initial blood cardioplegic reperfusion. CONCLUSION: Asanguineous cardioplegic washout before blood cardioplegic reperfusion limits oxygen utilization during subsequent controlled reperfusion, restricts early recovery of systolic shortening, allows more myocardial edema, and produces extensive histochemical damage, which may be avoided by initial reoxygenation with blood cardioplegia. The red blood cells appear more important than the plasma components of blood cardioplegia. 