Background: People with post COVID-19 syndrome (PCS) commonly complain of tachycardia and worsening of symptoms even after mild activity. However, the relationship between heart rate (HR) and physical activity (PA) in this population is still poorly understood. Objectives: To describe the relationship between HR and PA in people experiencing PCS. Methods: This observational study used data from participants with PCS (≥3 months post infection) collected using wearable devices (accelerometer and Garmin smart watch) over 4 days while performing daily activities. Main variables analyzed included time in different PA intensity levels (sedentary, light, moderate to vigorous (MVPA)), step count, average daily HR, and percentage of time in tachycardia (>100 beats per minute). Results: Sixteen participants had complete data and were included. The mean age of participants was 51±12 years (13 females). Average daily step count was 3462±1831. Average HR and percentage of time in tachycardia were 85±7 bpm and 13.7±10 % respectively. Daily step count was inversely correlated with average daily HR (r = -0.544, p = 0.030). Average daily HR gradually increased across PA levels from sedentary to MVPA (p = <0.001). Percentage of time in tachycardia was significantly lower at the MVPA level compared to the sedentary level after adjusting for age and sex (p = 0.027). Conclusion: PCS patients experience greater percentage of time in tachycardia while doing little to no activity compared to when they are engaged in higher intensities of PA. PCS patients experience greater periods of tachycardia while doing little to no activity compared to higher intensities of PA. Healthcare professionals should consider these findings, as traditional rehabilitation approaches may not be optimal for this group due to tachycardia experienced at rest or at low intensities of activity. It is crucial to design rehabilitation protocols that are both safe and suitable for the specific needs of post COVID-19 patients.