Aim, materials and methods <p>Obstructive sleep apnea (OSA) leads to organ ischemia, including that of the heart. The aim of this study was to assess the frequency of OSA by polygraphic examination in patients admitted with acute coronary syndrome, to evaluate the influence of OSA on echocardiographic findings and myocardial infarction markers and to describe the influence of CPAP treatment on OSA parameters and echocardiographic indices after myocardial infarction. We included 25 patients treated with primary coronary angioplasty, aged 60.3 ± 19.4 years, with a BMI of 32.2 ± 3.8.</p> Results <p>Polygraphy showed OSA in 18 (72%) patients, and in 12 (48%) severe OSA (AHI &gt; 30) was diagnosed. OSA predominantly affected obese patients (BMI &lt; 30, <i>n</i> = 13: AHI 23.2 ± 17.4, BMI ≥ 30, <i>n</i> = 12: AHI 55.5 ± 23.6, <i>p</i> &lt; 0.000001). In patients with normal RV structure and function AHI was significantly lower compared to those with RV dysfunction. In patients without OSA, CKMB and troponin levels were significantly lower as compared to those with OSA: AHI &lt; 15: CKMB 41.7 ± 40.7, Tn 0.84 ± 1.0; AHI≥15: CKMB 169.2 ± 112.4, Tn 4.77 ± 4.43; <i>p</i> = 0.04. CPAP therapy was started only in 9 (50%) patients with OSA due to low patient compliance. In patients treated with CPAP, the therapy resulted in a significant decrease in OSA indices (AHI dropped from 52.0 ± 18.6 to 5.0 ± 1.0; <i>p</i> = 0.001). The function of the RV, as measured by TAPSE, improved only in patients treated with CPAP (CPAP: from 20.5 ± 3.3 to 22.3 ± 2.3, <i>p</i> = 0.04; no CPAP: 22.3 ± 4.7 to 23.6 ± 1.8; p–ns).</p> Conclusions <p>We demonstrate a high prevalence of OSA in patients presenting with acute coronary syndrome. OSA influences RV enlargement and dysfunction, as well as CKMB and troponin levels during myocardial infarction. After myocardial infarction, RV function improves only in patients treated with CPAP.</p>