Although coronary risk factors promote the formation of atherosclerotic plaque containing activated platelets and inflammatory leukocytes, and play a pivotal role in the development of coronary artery diseases (CAD), the hemorheological effects of these risk factors on circulating intact erythrocytes, a major component of whole blood cells, are poorly understood. Therefore, this study aimed to quantify erythrocyte deformability in patients with coronary risk factors, and enrolled 320 consecutive cardiac outpatients including 33 patients with nonvalvular atrial fibrillation (AF). Patients with acute coronary syndrome or valvular AF were excluded. Demographic variables obtained by medical records were correlated with erythrocyte deformability investigated by our highly sensitive and reproducible filtration technique. Among demographic variables, triglyceride (p = 0.004), HbA1c (p = 0.014) and body weight (p = 0.020) showed significant inverse correlation to the erythrocyte deformability. This deformability was not associated with types of CAD (old myocardial infarction vs. stable angina) or modality of treatment (percutaneous intervention vs. coronary artery bypass grafting). Unexpectedly, stepwise multiple regression analysis demonstrated that nonvalvular AF was the most significant contributor to the impaired erythrocyte deformability (p = 0.002). Hypertension and dyslipidemia are more prevalent in the AF patients (p < 0.001), and the erythrocyte deformability was found to be impaired synergistically and significantly (p < 0.001) during the stepwise accumulation of the coronary risk factors in addition to AF. In conclusion coronary risk factors synergistically impair the erythrocyte deformability, which may play an important role in critically stenotic coronary arteries. Since the impairment of intact erythrocyte deformability is mostly associated with nonvalvular AF, this common arrhythmia may reflect the coronary risk accumulation.