Formula car racing is highly competitive and induces significant physical stress. Previous studies have shown that intense physical stresses, such as g-force, accelerate the driver's heart rate (HR). In contrast, it remains unclear whether psychological stress affects the physiological states of racers and racing performance. To investigate this phenomenon, we developed a wearable monitor that can track the driver's HR during a race. The HR and driving performance of two professional drivers were monitored in real racing situations. Changes in HR were then evaluated based on changes in the racing situation and car behavior. The results suggest that HR acceleration is strongly correlated with race situations such as free practice or qualifying sessions, and that such changes are related to subsequent driving performance.