Background <p>Obstructive sleep apnea is a chronic disorder that results in many cardiovascular disorders including hypertension and arrhythmias. Cardiopulmonary exercise testing (CPXT) has been used for measuring VO₂, VCO₂, and VE. This may have clinical utility if added to polysomnography used to identify OSA.</p> Aim of study <p>To assess altered ventilatory response and heart rate recovery in response to exercise in patients with obstructive sleep apnea and their relation to its severity.</p> Patients and methods <p>Case control study was enrolled including 30 OSA patients divided into (5 mild, 8 moderate, and 17 severe) and 15 healthy control. The two groups underwent cardiopulmonary exercise testing and different parameters were calculated.</p> Results <p>Greater VE, VE/VCO₂, VE/VO₂ ratios, and VE/VCO₂ slope were statistically significant regarding the patients group compared to control group (<i>p</i> &lt; 0.001, <i>F</i> ¼ 69.053, 104.381, 140.806, and 68.010, respectively. OSA patients had a reduced maximal exercise capacity expressed as lower VO₂ peak, decreased BR and VO₂ at anaerobic threshold compared to control group (<i>p</i> &lt; 0.001, <i>F</i> ¼ 22.597, 68.773, and 82.90, respectively). Delayed HRR and weaker CR in patients with OSA than in controls with negative relationship to severity of OSA were proved (<i>p</i> &lt; 0.001, <i>F</i> ¼ 119.493 and 91.271, respectively). The study revealed elevated max SBP, max DBP, and recovery SBP in the following 2 min after exercise in patients with OSA relative to their healthy controls with positive relationship to the severity of OSA (<i>p</i> &lt; 0.001, <i>F</i> ¼ 37.129, 169.275, and 244.609, respectively).</p> Conclusion <p>Patients with OSA demonstrated exaggerated ventilatory response to exercise and autonomic dysfunction.</p>