The aim of this study was to test whether an improvement of left ventricular ejection fraction (EF) in the early phase after acute myocardial infarction is associated with a reduction of the severity of central and obstructive sleep apnoea. 40 consecutive patients with acute myocardial infarction underwent polysomnography and cardiovascular magnetic resonance imaging within 5 days and 12 weeks after the event to assess sleep apnoea and cardiac function. We stratified the sample in patients who improved their left ventricular EF within 12 weeks by ≥ 5% (improved EF group, ΔEF 9 ± 1%, n=16) and in those who did not (unchanged EF group, ΔEF -1 ± 1%, n=24). Prevalence of sleep apnoea (≥ 15 apnoea and hypopnoea events·h(-1)) within ≤ 5 days after myocardial infarction was 55%. Apnoea and hypopnoea events·h(-1) were significantly more reduced in the improved EF group compared with the unchanged EF group (-10 ± 3 versus 1 ± 3 events·h(-1); p=0.036). This reduction was based on a significant alleviation of obstructive events (-7 ± 2 versus 4 ± 3 events·h(-1); p=0.009), while the reduction of central events was similar between groups (p=0.906). An improvement of cardiac function early after myocardial infarction is associated with an alleviation of sleep apnoea. This finding suggests that re-evaluation of treatment indication for sleep apnoea is needed when a change in cardiac function occurs.