BACKGROUND: Coronary artery enlargement has been previously described in left ventricular hypertrophy. OBJECTIVES: We sought to assess coronary artery dimensions and their relation to left ventricular muscle mass in primary and secondary hypertrophy. METHODS: Cross-sectional area of the left and right coronary arteries was determined by quantitative coronary angiography in 52 patients: 12 control subjects and 40 patients (13 with hypertrophic cardiomyopathy, 12 with dilated cardiomyopathy and 15 with aortic valve disease). As a measure of left ventricular hypertrophy, angiographic left ventricular mass and equatorial cross-sectional muscle area were determined. RESULTS: Cross-sectional area of both the left and right coronary arteries is increased in left ventricular hypertrophy (p < 0.05 vs. values in control subjects). There is a curvilinear relation between left coronary artery size and left ventricular muscle mass (r = 0.76) or cross-sectional muscle area (r = 0.75). However, normalization of coronary cross-sectional area for left ventricular muscle mass or muscle area shows insufficient enlargement of the coronary arteries in both primary and secondary hypertrophy. CONCLUSIONS: 1) Coronary artery size increases as left ventricular mass increases in both primary and secondary hypertrophy. 2) The enlargement of left coronary cross-sectional area is independent of the cause of the increase in left ventricular mass. 3) The size of the coronary arteries is inappropriate with regard to left ventricular hypertrophy. Thus, the stimulus for growth of the coronary arteries is not influenced by the underlying disease but appears to depend on the degree of left ventricular hypertrophy.