To assess the role of arterial hypertension in the development of coronary collateral circulation in relation to coronary artery disease, severity and left ventricular function, we studied 433 men with angiographically documented coronary artery disease. Of these, 122 showed disease in one vessel, 157 showed disease in two vessels and 159 patients showed disease in three vessels; 153 (35.3%) patients had arterial hypertension. The hypertensive patients had a similar distribution of diseased coronary vessels and similar coronary obstruction scores according to Gensini compared with the normotensive patients (64 versus 62, NS), but they had higher left ventricular ejection fraction values (51.5 versus 46.8%, P = 0.002). Coronary collateral circulation was more often seen in hypertensives (70.6 versus 57.1%, P = 0.006), especially high-grade coronary collateral circulation (27 versus 15%, P = 0.001). However, patients with coronary collateral circulation had more severe coronary artery disease, whether they had arterial hypertension (71 versus 46, P = 0.00008) or not (76 versus 43, P less than 0.00001). Thus, for a similar severity of coronary artery disease, patients with arterial hypertension and also coronary collateral circulation had higher ejection fraction values (52.6 versus 46.1%, P = 0.0006). This was more readily observed in those patients with disease in three vessels and coronary collateral circulation (52 versus 42.8%, P = 0.002). Patients without coronary collateral circulation had similar ejection fraction and coronary obstruction score values, irrespective of arterial hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)