Background: Evidence of cardiopulmonary resuscitation (CPR) performance has driven interest in procedures, e.g., debriefing to improve CPR quality. Aim: To investigate retention of skills with and without debriefing 3-months after CPR training on high-fidelity manikins (HFM) among participants involved in the "Heart Safe City Initiative" event (HSCI) in Makkah, Saudi Arabia. Methodology: A randomized controlled design was used during October 2017-January 2018. Participants were divided into two groups: an intervention group to receive debriefing after CPR (debriefing group or "subjects"), and a non-intervention group ("controls"). Participants were tested repeatedly: before training (pre-training test), immediately after and 3-months after training (retention or late test); and scores for each test were recorded. Results: The study's subjects and controls did not vary by age, sex, nationality, and profession's criteria (p > 0.05, all analyses). The mean retention posttests scores significantly varied between subjects and controls [t(df = 200) = 27.7, p < 0.0001)]; however, the two groups did not vary in their immediate score levels (mean ranks: 106.77 v. 95.68, p = 0.18). Further, the immediate posttest scores were significantly higher than the pretests' within the study population as a whole group [mean difference 38.05% ± 27.59%, t(df = 201) = 13.5, p < 0.001]; within subjects [mean difference 40.68% ± 29.26%, t(105) = 14.31, p < 0.0001]; and within controls [mean difference 35.06% ± 25.