Eleven cases of spontaneous hypoglycaemia in congestive heart failure in adults are reported. There were 5 males and 6 females, aged from 15 to 65 years (mean, 44 years). Blood sugar ranged from 2 to 42 mg/100 ml (mean 21 mg/100 ml). Six patients were in coma on admittance, 1 was confused, and 4 were conscious. The underlying condition was rheumatic valvular heart disease (3), chronic obstructive lung disease (4), cornonary heart disease (3) and cardiomyopathy (1). Five of the 11 patients died. The mechanism of hypoglycaemia is discussed and thought to be a combination of factors such as liver dysfunction, low calorie intake, malabsorption, and increased glusose utilization by ischaemic tissues, including the heart. It is recommended that in patients with congestive heart failure presenting with coma or confusion, blood sugar should be checked for possible hypoglycaemia.