Literally 'heart and guts' — your deep inner nature. Chinese associates both the heart and the gut with emotions and character, similar to English 'gut feeling.'
心肠 almost always appears with an adjective: 好心肠 (kind-hearted), 坏心肠 (malicious), 铁石心肠 (heart of stone), 软心肠 (soft-hearted). It describes someone's fundamental nature, not a temporary mood.
