The purpose of the present study was to determine the effectiveness of work rate to heart rate ratio at the estimated anaerobic threshold (A[subscript T]). Thirty male subjects performed an incremental exercise test (15 W/min) until the limit of tolerance was reached. Ventilatory and gas exchange parameters were evaluated breath-by-breath and the heart rate was recorded. A[subscript T] was estimated from the work rate heart rate ratio and compared with the V-slope method. A deviation from linearity in heart rate was observed only in 4 subjects (13%) and 3 of them (10%) associated with A[subscript T]. All other 26 subjects showed linear increase in heart rate to work rate relationships (87%). The O[subscript 2] uptake at the estimated A[subscript T] using V-slope break point was found to be 1.95 ± 0.2 L/min (65% of maximal O[subscript 2] uptake). Absence of a break point in heart rate work rate relationship (87%) and an extremely low percentage of association in A[subscript T] estimation between the Conconi and V-slope methods (10%) may reduce the reliability of the Conconi test. Thus, caution should be taken by investigators using this technique, especially when making important decisions for patients and sports training.