Measures of heart rate variability (HRV) are hypothesized to provide indices of mental engagement (ME). HRV and perceived workload were measured to determine whether ME is moderated by task type, processing demands, and practice. Twenty four (22+/-3yrs.) participants were assigned to groups that performed either two executive-processing (EF) tasks or two non-executive processing (NEF) tasks. Across 3 sessions, participants practiced a cognitive computer-based cognitive task and a psychomotor task. HR was recorded for 5-min epochs before and during each task; workload ratings were recorded following each task. ANOVAs revealed that participants\' HRV decreased when performing cognitive and psychomotor tasks; the decline was greater, however, for NEF tasks. Over sessions, HRV increased during EF but not NEF tasks; workload scores lessened during EF but not NEF tasks. ME was intensified when participants learned novel cognitive and psychomotor tasks; however, the intensity level depended on the task, and its maintenance was altered with practice.