The Hers-Vif (French pronunciation: [ɛʁs vif], "Live Hers", as opposed to the slower flowing Hers-Mort, "Dead Hers"), also named Grand Hers or simply Hers, is a 135-kilometre (84 mi) long river in southern France, right tributary of the Ariège.

[1] The Hers-Vif rises at an elevation of about 1,500 metres (4,900 ft) near the Chioula Pass of the Pyrenees, approximately 6 kilometres (4 mi) north of Ax-les-Thermes.

It is the major tributary of the Ariège into whose right bank it flows 2 kilometres (1.2 mi) upstream from Cintegabelle in the Haute-Garonne.

It flows some 30 kilometres (19 mi) through the Pyrenees, descending 1,100 metres (3,600 ft) to the village of Peyrat, where it reaches a piedmont plain.

Several rivers flow into it: Departments and towns along its course are: The Hers is probably known as vif (intense or rapid in this context) because of its sometimes spectacular floods – that of 16 June 1289 having entirely destroyed Mirepoix.