BACKGROUND In patients with heart failure, death is often sudden due to life-threatening arrhythmias. This work was carried out to evaluate the pattern of arrhythmias in Nigerians with heart failure. METHODS Thirty subjects with congestive heart failure (CHF), 30 subjects with hypertensive heart disease, and 15 normal subjects with no obvious features of heart disease were evaluated with resting and 24-hour electrocardiographic monitoring and transthoracic echocardiography. Data were analyzed with one-way analysis of variance with post hoc Duncan's analysis, Fisher's exact test, and linear regression analysis using SPSS version 16. RESULTS CHF subjects had more instances of supraventricular tachycardia (P=0.005), ventricular extrasystoles (P<0.001), bigeminy (P<0.001), trigeminy (P<0.001), couplets (P<0.001), triplets (P<0.001), and nonsustained ventricular tachycardia (VT) (P=0.003) than the other two control groups. They also showed a significantly longer VT duration (4.6±5.6 seconds) compared with the other groups (P<0.001). Linear regression analysis showed a significant direct relationship between VT and the maximum number of ventricular extrasystoles per hour (P=0.001). CONCLUSIONS Cardiac arrhythmias are common in subjects with CHF and are more frequent when compared with patients with hypertensive heart disease and normal subjects.