We investigated whether parasympathetic tone may affect ischemic preconditioning in terms of ST segment alteration during coronary angioplasty. Coronary balloon angioplasty was performed in 19 patients with angina and isolated right coronary artery disease. Parasympathetic tone was assessed by frequency domain parameters of heart rate variability using 24-hour electrocardiographic recordings obtained before angioplasty. Logistic regression analysis showed the high frequency component to be an independent predictor of the change in ST elevation induced by the second balloon inflation. An increase in parasympathetic tone was related to ischemic preconditioning with respect to the electrocardiographic alterations observed in these patients.