The present study examined the relationship between heart rate (HR) changes accompanying isometric and isotonic exercises and HR changes during attempted voluntary HR acceleration. Substantial cardiac accelerations accompanied both types of exertion, with the isotonic exercise attracting the larger magnitude HR changes. Significant HR increases were also observed during attempted voluntary HR acceleration both with and without feedback; however, feedback prompted larger HR increases than instructions alone. The HR changes accompanying both types of exercise reliably predicted the extent of voluntary HR increase but only for the condition in which feedback was available. This occurred in spite of the absence of observable EMG changes during attempted HR acceleration. Changes in respiration rate during voluntary HR increase were highly correlated with changes in HR. A similar co-variation occurred with the isotonic exercise but was absent with the isometric exercise. The results are discussed in terms of the possible mediational mechanisms underlying voluntary HR acceleration.