Cardiovascular diseases are among the leading causes of mortality worldwide, making continuous electrocardiographic (ECG) monitoring essential for the early detection and follow-up of cardiac abnormalities. This study presents an Internet of Things (IoT) platform for continuous remote monitoring of three-lead ECG signals using LTE-M cellular connectivity. The proposed system integrates an ADS1293 analog front-end for ECG acquisition, a Walter IoT Module for MQTT-based data transmission, and a cloud infrastructure for secure data reception, storage, and visualization. A dual-core implementation on the ESP32 separates ECG acquisition from MQTT communication, preventing sample loss during continuous monitoring. Experimental results demonstrated reliable transmission of raw three-lead ECG signals, with no packet loss observed during a continuous 12 h LTE-M transmission test involving approximately 250,000 packets. The monitoring mechanism also automatically detected packet losses and device restarts. At the same time, server performance evaluation showed low CPU and memory utilization during simultaneous communication with five data sources under the evaluated conditions. These results validate the proposed IoT communication platform and establish a foundation for future work, including intelligent ECG analysis, improvements in signal acquisition and conditioning, and the continued development of the portable Holter device.