Empathy, a core process for social interactions, is the capacity to understand and share others’ mental states and emotions. Each individual is thought to have a maximum level of empathy (empathic ability) and a spontaneous tendency to express it (empathic propensity), which can be affected by multiple factors. Two within-subject studies were conducted to assess the malleability of empathy by modulating contextual factors and measuring their interaction with psychological characteristics. In Study 1, 59 healthy adults evaluated their empathy for people showing facial expressions of pain following different instructions: Passive Observation and Instruction to Actively Empathize. In Study 2, 56 healthy adults performed a similar task under two conditions: Passive Observation and Observation under a Cognitive Load. The results revealed that empathy was significantly increased in the actively empathizing condition (Study 1) and under a cognitive load, but more importantly for men (Study 2). The level of change between the two conditions was associated with self-reported empathy, autistic, alexithymia and psychopathic traits (Study 1), as well as with working memory capacities and the level of empathy reported in the passive observation condition (Study 2). These findings suggest that an instruction to actively empathize and, surprisingly, a cognitive load can both increase empathy, but not for the same individuals. An instruction to actively empathize seems to increase empathy for individuals with good empathic dispositions, while a cognitive load enhances empathy in people for which empathic propensity is sub-optimal.