Hypertrophic obstructive cardiomyopathy (HOCM) is still a serious problem that is characterized by an increasing hypertrophy of the cardiac muscle. The aim of this study was to investigate the hypothesis whether in HOCM the coronary flow reserve in the left anterior descending artery (LAD) is influenced by pharmacologic stimulation or stimulation using a pacemaker. The study was carried out in 15 patients (6 male, 9 female) with the typical echocardiographic signs of HOCM without coronary artery disease. Using an intracoronary Doppler catheter the average peak velocity and the absolute coronary flow reserve were determined in the proximal, medial and distal part of the LAD under influence of Papaverine, Substance P and under pacemaker stimulation. The coronary square plane was calculated angiographically under the influence of Substance P. Moreover, the retrograde flow was studied and the coherence between the increase of the coronary square plane and the coronary flow reserve were investigated. For statistical analysis the mean value, the standard error of the mean, Spearman's correlation coefficient and the t-test were calculated. Under pharmacologic stimulation higher values in the average peak velocity were observed compared to pacemaker stimulation. A retrograde flow was observed in 8 out of 10 patients. The coronary flow reserve was higher under pharmacologic influence than under pacemaker stimulation. A coherence between the increase of the coronary square plane and the coronary flow reserve was not found. So far, from the published data concerning the characteristics of coronary flow in HOCM patients, only the retrograde flow was reproducible in our patient group. However, a decrease of the coronary flow reserve compared to a healthy control group of the literature could not be observed. Nevertheless ischemia in the subordinate vessels and on the base of microcirculation cannot be excluded.