Heart rate is often, but not always, lower during exercise in the cold. The linear relationship between heart rate and oxygen consumption is displaced such that at a given rate oxygen uptake is higher. Cardiac arrhythmias are more frequent in the cold. Stroke volume tends to be higher than under warmer control conditions, but may decline sooner or at a rate equivalent to warm controls at heavy workloads. Cardiac output is similar to the same work done in temperature environments.