Due to the current ubiquity of oncological diseases, the second leading cause of death in Croatia, but also in most developed countries, the use of systemic oncological therapy is growing. Although it seems much more benign compared to the surgical and radiotherapy approach, it also causes a number of side effects. One of them is cardiotoxicity. Cardiotoxicity may not be such a common side effect, but its consequences can be very severe. One form of cardiotoxicity evaluation is the measurement of the electrical heart activity via an ECG. Its changes were most often observed with the use of classical chemotherapeutics such as antracyclins, alkylating cytostatics and platinum compounds and somewhat less frequently with the use of smart drugs. The most common changes observed in most drugs were arrhythmias of various forms. Also, the prolongation of the QTc interval was very present, and changes in the ST segment, T and P waves and decreased voltage of the QRS complex occurred somewhat less frequently. Cardiotoxicity has been shown to be dose-and duration-dependent, but all have roughly the same conclusion that cardiac parameters should be monitored regularly and in case of any change, the cause must be determined and the therapy permanently or temporarily discontinued.