The effect of nifedipine on tension, coronary flow and perfusion pressure was studied in the Langendorff rabbit heart after 15 and 60 min global ischaemia. Nifedipine (1.44 X 10(-8) M) added to the perfusate before 15 min ischaemia prevented the increase of diastolic coronary resistance which occurred on reperfusion in the absence of the drug. The recovery of force of contraction was unaltered. There was no change in the increase in resistance on reperfusion if nifedipine (1.44 X 10(-8) M) was given at the time of reperfusion after 15 min ischaemia. Ventricular fibrillation on reperfusion was prevented if nifedipine was added before 15 min of ischaemia. After a more prolonged period of ischaemia (60 min) the rise of resting tension on reperfusion was not prevented by giving nifedipine (1.44 X 10(-8) M or 1.44 X 10(-7) M) before ischaemia, although the rise during ischaemia was delayed. Both concentrations of nifedipine reduced the increase in diastolic coronary resistance which occurred on reperfusion. These results suggest that nifedipine, in a concentration close to the therapeutic range, increases coronary reperfusion after global ischaemia. This represents one mechanism by which nifedipine can have a beneficial effect on the ischaemic myocardium.