Aims: The implantation of percutaneous atrial septal occluder (ASO) devices for patent foramen ovale (PFO) may affect left atrial (LA) function. Some studies have reported short- to mid-term impairment of this function, though it remains unclear whether this is a transient or permanent negative effect, nor if all patients are equally susceptible to these changes. Methods and results: Observational, prospective study of consecutive patients with cryptogenic stroke (CS) undergoing percutaneous closure of PFO. Echocardiographic evaluation of evolving structural and functional parameters of the LA was carried out before procedure, inmediately after (within 24 hours), 6 and 18 months after device insertion. From March 2019 to October 2023, 170 patients with CS were enrolled, 82 eligible for PFO closure and 65 undergoing percutaneous closure. Baseline structural and functional parameters were within normal limits. At 6 months follow-up, there is a significant increase in LA volumes and a deterioration of reservoir and conduit functions measured by strain. There is a subsequent trend toward normalization, but baseline parameters are not reached by 18 months. Conclusions: PFO device closure negatively impacts on LA function, resulting in increased atrial volumes, worsening of left ventricular diastolic function, decreased reservoir and conduit function, and a compensatory increase in pump function. These changes are significant at 6 months, with partial improvement but without full normalization of parameters at 18 months follow-up.