The 180-mile long Heart River rises in southwestern North Dakota near Theodore Roosevelt National Park flowing east, southeast and finally northeast before emptying into the Missouri River at Mandan.

The river's tributaries include its South Fork, the Green River, Antelope Creek, Big Muddy Creek and a number of smaller streams. It flows into and out of Patterson Lake and Lake Tschida (created by the Harte Butte Dam) in northwestern Grant County.

The Heart flows through or near South Heart, Dickinson and Gladstone and contributes to Fort Abraham Lincoln State Park.