Lacosamide is an antiepileptic drug used to treat partial-onset seizures. While it is generally well-tolerated, there have been some reports of heart complications associated with its use. According to DrugPatentWatch [1], one of the potential side effects of lacosamide is cardiac arrhythmia, which is an abnormal heart rhythm. This side effect is listed as rare, occurring in less than 1% of patients.

A study published in the Journal of Clinical Neuroscience [3] investigated the cardiac safety of lacosamide in patients with epilepsy. The study found that lacosamide was generally well-tolerated, but there were some cases of cardiac adverse events, including sinus bradycardia (slow heart rate), atrioventricular block (a disruption of the electrical signals between the heart's chambers), and QT prolongation (a potentially life-threatening heart rhythm disorder).

Another study published in Epilepsy Research [2] also investigated the cardiac safety of lacosamide. The study found that lacosamide did not significantly affect cardiac function in patients with epilepsy, but noted that there were some cases of QT prolongation and sinus bradycardia.

In summary, while lacosamide is generally well-tolerated, there have been some reports of cardiac adverse events associated with its use, including cardiac arrhythmia, sinus bradycardia, atrioventricular block, and QT prolongation. Patients taking lacosamide should be monitored for these potential side effects.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LACOSAMIDE
[2] https://pubmed.ncbi.nlm.nih.gov/25046031/
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8790938/