Heat stress induces failures in the physiological mechanisms that regulate the body temperature of farm animals and causes a loss in their productive and reproductive potential. Thus, we performed a scoping review to systematically map, describe, and classify primary research that assessed the effect of heat stress on the reproductive, physiological, and productive parameters of livestock. Electronic databases were searched to retrieve full-text, peer-reviewed experimental or cohort studies published from 1980 to August 2018. We included in vivo and in vitro studies exposing animals or cells to heat stress conditions and used a control group. Studies were evaluated based on title and abstract and then selected for final inclusion based on full text. We performed data charting to describe and visualize the evidence. In total, we included 466 studies, among which bovines and porcines were the most frequent species studied. Reproductive and physiological parameters were the main groups of outcomes assessed, and studies using adult females predominated. Seventy percent of the studies were experimental, and almost half of the studies used natural environmental conditions to assess the effect of heat stress in animals. Most of the studies were performed in the Americas and Asia, and three journals provided one-third of the publications. The systematic evidence synthesis presented herein outlines the trends of research performed to assess the effect of heat stress on livestock and allowed us to define future secondary studies to extend our knowledge about the negative impact of heat stress on the productivity of farm animals.