Total physical activity energy expenditure is a determinant of weight loss and risk factor modification in adults. There has been very little study of physical activity energy expenditure in cardiac rehabilitation populations. Exercise-related energy expenditure was calculated in 112 patients with coronary artery disease in an outpatient cardiac rehabilitation program. Gross energy expenditure was estimated with the heart rate/oxygen consumption relation as measured during metabolic exercise testing with expired gas analysis. The average exercise training energy expenditure (ETEE) per cardiac rehabilitation exercise session was quite low at 270 +/- 112 kcal. Baseline fitness level (peak oxygen consumption), body weight, total exercise duration per session, age, and body mass index were all significant determinants of ETEE (r = 0.56 to -0.37, all P <.01). Additionally, patients who had undergone coronary bypass surgery and patients with medical comorbidities expended significantly fewer calories during exercise. In women, there was a relation between ETEE and change in total and LDL cholesterol (r = -0.43 and -0.45, respectively), although no such relation was observed in men. Cardiac rehabilitation exercise training, as currently structured, burns surprisingly few calories and has little impact in the short term (3 months) on measures of obesity and lipid risk factors. Alternative training programs should be considered to maximize caloric expenditure and modify specific risk factors such as obesity and dyslipidemia.