Various fixation techniques for implantable medical device (IMDs) are described. In one example, an assembly comprises an IMD; and a set of active fixation tines attached to the IMD. The active fixation tines in the set are deployable from a spring-loaded position in which distal ends of the active fixation tines point away from the IMD to a hooked position in which the active fixation tines bend back towards the IMD. The active fixation tines are configured to secure the IMD to a patient tissue when deployed while the distal ends of the active fixation tines are positioned adjacent to the patient tissue.