Heart River, Mountain brook in Yellowstone National Park, United States.

Heart River is a mountain brook in Yellowstone National Park that originates from the Continental Divide in the Rocky Mountains near Yellowstone Lake. The water flows south through a narrow valley before eventually joining the Snake River.

The Heart River drains Heart Lake, which sits on the Continental Divide a few miles southeast of Yellowstone Lake, and its whole 4.8-mile course lies inside Yellowstone National Park. It leaves the lake's southeastern end, takes two tributary streams from the northeast, and drops through a short, steep gorge before running about 4 miles south to the Snake River near the Teton National Forest boundary, at 2,217 m. The park itself dates from 1872.

The Heart River and its surrounding area serve as research locations for geological studies and environmental monitoring within the national park system.

The river's entire 4.8-mile course lies inside Yellowstone National Park, from Heart Lake to its mouth on the Snake River at 2,217 m. The Heart Lake Trail runs along the lake's shore, and the river leaves the lake through a short, steep gorge. The Snake River boundary with Teton National Forest is near the confluence.

Heart River drains a basin of 78 km² and drops to an outlet elevation of 2,217 m where it meets the Snake, just outside the Teton National Forest boundary. Its name comes from Heart Lake, the body of water at its source on the Continental Divide.