Warm-up phenomenon in angina pectoris.

The warm-up phenomenon, in which the second of two successive exercise tests manifests less ischaemia than the first, was studied to find out whether it results from decreased myocardial oxygen consumption or from increased coronary-artery blood-flow during the second test. Patients performed an initial exercise test, then continued to exercise for 30 minutes after which they rested for 20 minutes. They then repeated the exercise test with a work load and duration identical to the first. 21 (95%) of 22 patients tested with a bicycle and 9 (75%) of 12 patients tested by a modified two-step test had less electrocardiographic evidence of ischaemia on the second test than on the first. Rate-pressure products at peak exercise suggested that the lessened ischaemia was not due to decreased mnyocardial oxygen consumption. Rather, the warm-up phenomenon seemed to result from increased coronary flow. It can be evoked in most patients who have an ischaemic response to exercise.