Impedance to flow due to coronary spasm is currently interpreted as the mechanism of Prinzmetal angina. Flow impedance, probably of vasomotor origin, superimposed on severe coronary stenosis is also viewed as the trigger for the spontaneous component of mixed angina. The major question that we attempted to answer in this study was whether mixed angina may be considered a variant of the Prinzmetal form, or a particular manifestation of the classic effort form. For these purposes we investigated the acute vasomotor response to calcium channel blockade (nifedipine 10 mg sl) of both significant (greater than 50%) stenotic lesions and of normal coronary vessels in 22 patients with mixed angina and in 14 patients with Prinzmetal angina, and correlated it with the clinical response to treatment (nifedipine 20 mg qid). Calcium channel blockade, in fact, is considered as a specific remedy in the presence of an altered coronary vasomotility. The clinical response was evaluated through ambulatory Holter monitorings of 48 hour duration, while on placebo, nifedipine and placebo again. In mixed angina an angiographic evaluation showed that the residual lumen diameter of significant lesions was unchanged in 2, enhanced in 11 and reduced in 9 patients after sl nifedipine; lumen variations from base line ranged from +1.5 to -1.3 mm. Acute stenosis widening or narrowing correlated closely with the efficacy or not of the treatment. In the Prinzmetal group the vast majority of the lesions had compliant portions which invariably responded with dilatation (the residual coronary lumen increased by an average of 69% of base line); 100% of patients in this group responded favourably to treatment.(ABSTRACT TRUNCATED AT 250 WORDS)