Obstructive sleep apnea (OSA) is associated with cardiovascular diseases, yet available data suggests cardiologists underreport OSA. This study assessed whether cardiologists' knowledge and attitudes about OSA contribute to this finding. A previously validated questionnaire, the "Obstructive Sleep Apnea Knowledge and Attitudes Questionnaire" (OSAKA), was modified by the addition of 20 knowledge items and one attitude question to include a total of 38 knowledge items and six attitude questions. The questionnaire was mailed to a random sampling of 420 cardiologists in the USA. Ninety-two cardiologists (22%) returned completed questionnaires. Mean age was 48 +/- 10 years, 74% were male, and 52% were general cardiologists. Mean score on the original OSAKA portion of the questionnaire (76%) was similar to previously reported scores of primary care physicians (PCPs), while the total knowledge score was 77%. Scores did not differ by gender (p = 0.7) or subspecialty (p = 0.3), and there were no correlations between knowledge and age or years in practice. While 80% stated that identifying patients at risk for OSA was very or extremely important, only 68% felt confident identifying these patients, and only 18% felt confident managing OSA patients. There was no difference in mean total attitude score when analyzed by age, gender, years of practice, and subspecialty. Total knowledge scores correlated with attitude scores (r = 0.29, p = 0.004). Cardiologists' knowledge about OSA is comparable to that of PCPs. Cardiologists may lack confidence identifying and managing patients with OSA, factors that may contribute to their low rate of reporting OSA.