Communication between cardiologists and patients can significantly affect patient comprehension, adherence, and satisfaction. To our knowledge, a coaching intervention to improve cardiologist communication has not been tested. To evaluate the effect of a communication coaching intervention to teach evidence-based communication skills to cardiologists. This 2-arm randomized clinical trial was performed at outpatient cardiology clinics at an academic medical center and affiliated community clinics, and from February 2019 through March 2020 recruited 40 cardiologists and audio recorded 161 patients in the preintervention phase and 240 in the postintervention phase. Data analysis was performed from March 2022 to January 2023. Half of the cardiologists were randomized to receive a coaching intervention that involved three 1:1 sessions, 2 of which included feedback on their audio-recorded encounters. Communication coaches taught 5 skills derived from motivational interviewing: (1) sitting down and making eye contact with all in the room, (2) open-ended questions, (3) reflective statements, (4) empathic statements, and (5) "What questions do you have?" Coders unaware of study arm coded these behaviors in the preintervention and postintervention audio-recorded encounters (objective communication). Patients completed a survey after the visit to report perceptions of communication quality (subjective communication). Analysis included 40 cardiologists (mean [SD] age, 47 [9] years; 7 female and 33 male) and 240 patients in the postintervention phase (mean [SD] age, 58 [15] years; 122 female, 118 male). When controlling for preintervention behaviors, cardiologists in the intervention vs control arm were more likely to make empathic statements (intervention: 52 of 117 [44%] vs control: 31 of 113 [27%]; P = .05); to ask, "What questions do you have?" (26 of 117 [22%] vs 6 of 113 [5%]; P = .002); and to respond with empathy when patients expressed negative emotions (mean ratio of empathic responses to empathic opportunities, 0.50 vs 0.20; P = .004). These effects did not vary based on patient or cardiologist race or sex. We found no arm differences for open-ended questions or reflective statements and were unable to assess differences in patient ratings due to ceiling effects. In this randomized clinical trial, a communication coaching intervention improved 2 key communication behaviors: expressing empathy and eliciting questions. Empathic communication is a harder-level skill that may improve the patient experience and information comprehension. Future work should explore how best to assess the effect of communication coaching on patient perceptions of care and clinical outcomes and determine its effectiveness in larger, more diverse samples of cardiologists. ClinicalTrials.gov Identifier: NCT03464110.