Information on rare adverse effects is often limited when a medication is initially approved for marketing. Medicines regulators use safety advisories to warn health professionals and consumers about emerging harms. This study aimed to identify characteristics and advice provided in cardiac safety advisories released by regulators in Australia, Canada, the United Kingdom, and the United States. This was a retrospective study of safety advisories about cardiac-related adverse events issued by these four international medicines regulators between 2010 and 2016. A descriptive overview was followed by a more detailed content analysis, focusing on recommended actions for health professionals, including monitoring advice. For the latter, we applied the systematic information for monitoring (SIM) scale to assess adequacy. Over this period, 164 safety advisories about cardiac harms were issued by the four regulators. There were 61 drugs with advisories of cardiac risk, only 9 (14.7%) of which had advisories from all regulators in countries where the drug was approved. The most common adverse events were cardiac arrhythmias (n = 97, 59.1%) and coronary artery disorders (n = 39, 23.8%). The most frequent advice to prescribers was to monitor patients (n = 74, 45.1%), although only 41.2% of these advisories provided detailed advice on how monitoring should occur. We found many differences in the decision to warn and the advice provided. Patient monitoring was most often recommended, but key information such as frequency or thresholds for action was often lacking. Healthcare professionals and consumers need consistent information about rare serious harms so that they can make informed decisions.