Background: Khat is a natural stimulant from the Catha edulis plant containing several chemical components, which can explain palpitation as a frequent symptom that develops during or after khat chewing. Aims: To study the effects of khat chewing on cardiac rhythm. Methods: We selected sixty khat-chewing Yemeni individuals and divided them into two groups: 30 were cardiac patients and the other 30 were non-cardiac individuals. All 60 individuals underwent 24 hours holter monitoring for 2 consequent days; the first was a khat-free day and the next was a khat-chewing day. The two groups were matched for age, sex, smoking habit, BSA, systolic and diastolic blood pressure. Non sustained Ventricular Tachycardia (VT) was defined as 3 or more wide QRS complexes at a rate of 120 beats/min and for a period less than 20 seconds. Results: The non-sustained VT was found on 7 (23.3%) of the 30 cardiac patients on a khat-chewing day compared to 2 patients (6.6%) on a khat-free day (p < 0.01). A significant difference was also seen among the normal individuals; 1 patient (3.3%) developed short runs of VT on a khat-chewing day compared to non VT on a khat-free day. Conclusions: 1) Serious arrhythmias occur in both cardiac and non-cardiac individuals during khat chewing days although they are more prominent among cardiac patients. 2) This may indicate beta-blocker usage for high risk khat chewers before khat chewing.