The QT interval is an electrocardiographical measurement that denotes the time interval between the commencement and completion of the cardiac ventricular contraction process. Alterations in its value indicate abnormal cardiac rhythm and herald the risk of torsades de pointes; a fatal ventricular arrhythmia. Causes leading to a prolonged QT interval encompass a heterogeneous gamut including genetic conditions, electrolyte imbalances, hormonal imbalances, and drugs. A wide range of drugs can lead to a prolonged QT interval and these include certain crucial drugs which are routinely prescribed by a pulmonologist for infectious as well as non-infectious pulmonary indications. This becomes particularly relevant in this decade which has witnessed an excrescence in drug-resistant tuberculosis cases. Certain vital drugs employed in its management prolong QT interval significantly. In these situations, the clinician faces the predicament of cautiously prescribing these drugs to eradicate the disease microbiologically whilst balancing the risk of sudden cardiac death due to torsades de pointes. We summarise the basics of QT interval which every pulmonologist presently needs to know.