In five patients studied 1 to 3 d after coronary artery surgery isoprenaline and nitroglycerine have been used to alter the systolic (TTI) and diastolic (DPTI) pressure time indices. A close correlation with the predicted relationship between diastolic coronary graft flow and the DPTI/TTI ratio has been demonstrated during isoprenaline-induced tachycardia. Nitroglycerine reduced diastolic coronary graft resistance and increased the DPTI/TTI ratio, effects which are desirable for the relief of angina.