BACKGROUND Although an increase in the occurrence of ventricular arrhythmias has been observed in hypertensive patients, some basic questions remain unresolved regarding the prevalence and the pathophysiology of these arrhythmias. The basic aims of this study were as follows: (1) to examine the incidence and severity of ventricular arrhythmias in a substantial number of hypertensive patients without electrocardiographic indications of hypertrophy; and (2) to examine the correlation between late potentials, hypertrophy, and ventricular arrhythmias in these patients. METHODS We studied 78 consecutive patients (31 men, 47 women), aged 60.5 +/- 7.8 years, with a history of hypertension but a normal electrocardiogram. All patients had an echocardiographic study, 24-hour ambulatory monitoring, exercise test, and signal-averaged electrocardiogram. The latter was analyzed using a 40- to 250-Hz filter and with a noise level < or = 0.3 microV. RESULTS Of the 78 patients studied, 21 (26.9%) had severe ventricular arrhythmias, while 57 (73.1%) had either no ventricular ectopics or sporadic isolated ventricular extrasystoles. Left ventricular hypertrophy, defined by echocardiography, was found in 58 patients (74.3%), of which 16 (27.58%) had severe ventricular arrhythmias. Five (25%) of the 20 patients without hypertrophy also had severe ventricular arrhythmias (P = NS). Ventricular late potentials were recorded in 19 (24.5%) of the 78 patients. Of these, 11 (57.89%) had severe arrhythmias, while of the 59 patients without late potentials 10 (16.94%) had severe ventricular ectopic activity. CONCLUSIONS In hypertensive patients without electrocardiographic signs of hypertrophy, the higher prevalence of ventricular arrhythmias does not appear to be related to left ventricular hypertrophy but is correlated with the existence of ventricular late potentials.