Holter monitoring was used to assess the incidence and characteristics of myocardial ischaemia immediately after successful coronary angioplasty in 24 patients. In 5 patients a total of 16 episodes of ST depression were recorded. All were asymptomatic but ranged from 4 minutes to over 20 hours in duration. These patients, however, made an uncomplicated recovery, as did 18 patients with no ischaemic episodes. In the remaining patient, initially labile, but then, fixed ST elevation, accompanied by chest pain occurred. Subsequent angiography demonstrated acute vessel occlusion. These labile ischaemic changes indicate that prior to complete occlusion the vessel may be in a dynamic state when antispasmodic and antithrombotic therapies may be of value.