Day–Night Variation of Acute Myocardial Infarction in Obstructive Sleep Apnea Fatima H. Sert Kuniyoshi, Arturo Garcia-Touchard, Apoor S. Gami, Abel Romero-Corral, Christelle van der Walt, Snigdha Pusalavidyasagar, Tomas Kara, Sean M. Caples, Gregg S. Pressman, Elisardo C. Vasquez, Francisco Lopez-Jimenez, Virend K. Somers We studied 92 patients with myocardial infarction (MI) for whom the time of onset of chest pain was clearly identified. An MI occurred between 12 am and 6 am in 32% of obstructive sleep apnea (OSA) patients and 7% of non-OSA patients (p = 0.01). The odds of having OSA in those patients whose MI occurred between 12 am and 6 am was 6-fold higher than in the remaining 18 h of the day (95% confidence interval: 1.3 to 27.3, p = 0.01). The diurnal variation in the onset of MI in patients with OSA is strikingly different; patients with nocturnal onset of MI have a high likelihood of having OSA.