The second Congress of Visegrád was a 1339 summit in Visegrád where it was decided that after the death of Casimir III of Poland, the son of Charles I of Hungary, Louis I of Hungary, would become King of Poland provided that Kazimierz does not have a son. This actually also happened.
When Casimir died in 1370 from an injury received while hunting, his nephew, King Louis I of Hungary, succeeded him as king of Poland in personal union with Hungary.
References
Congress of Visegrád (1339) Wikipedia(Text) CC BY-SA