Vectorcardiographic (VCG) studies were conducted in 71 patients with pure mitral stenosis (MS) documented by clinical findings, echocardiograms and cardiac catheterization. Among them, 31 were males and 40 females, with ages ranging from 20 to 58 (mean age 36.3) years. The Frank lead system was adopted for the VCG study. By VCG, 67 patients (94.4%) showed right ventricular hypertrophy (RVH), among whom 15 (21.2%) were type A, 30 (42.3%) type B and 22 (31.0%) type C. Forty-five patients (63.4%) were in sinus rhythm (NSR), while the remaining 26 (36.6%) were in atrial fibrillation (AF). Patients with type A RVH had a significantly higher pulmonary wedge (PAW) and main pulmonary arterial (MPA) pressures than those with type B or C. Patients with type C had a higher mean MPA pressure (39.0 +/- 11.3 mmHg) than those with type B (32.3 +/- 10.1 mmHg) (p less than 0.05). Among the 3 types of RVH, the mean right atrial (RA) pressures were similar (p greater than 0.05). Patients with AF had a lower mean MPA pressure, but a higher RA pressure than those with NSR (p less than 0.05). The maximal anterior force and maximal rightward force at the horizontal plane were significantly correlated with the mean MPA pressure (r = 0.54 and 0.49, respectively, both p less than 0.01), but they did not correlated well with the PAW and RA pressures (p greater than 0.05). We conclude that in patients with MS, as pulmonary hypertension progresses, VCG seems to begin with type B RVH, then emerges into type C and finally becomes type A.(ABSTRACT TRUNCATED AT 250 WORDS)