Purpose: Childhood cancer survivors are at risk for anthracycline-related cardiac dysfunction, often developing at a time when they are least engaged in long-term survivorship care. New paradigms in survivorship care and chronic disease screening are needed in this population. We compared the accuracy of a novel handheld mHealth platform (Vivio) as well as echocardiography for assessment of cardiac function [left ventricular ejection fraction (EF)] in childhood cancer survivors with cardiac magnetic resonance (CMR) imaging (reference). Experimental Design: Cross-sectional study design was used. Concurrent evaluation of EF was performed using Vivio, two-dimensional (2D) echocardiography, and CMR. Differences in mean EF (2D echocardiography vs. CMR; Vivio vs. CMR) were compared using Bland–Altman plots. Linear regression was used to evaluate proportional bias. Results: A total of 191 consecutive survivors participated [50.7% female; median time from diagnosis: 15.8 years (2–44); median anthracycline dose: 225 mg/m2 (25–642)]. Echocardiography overestimated mean EF by 4.9% (P < 0.001); linear regression analysis confirmed a proportional bias, when compared with CMR (t ¼ 3.1, P < 0.001). There was no difference between mean EF derived from Vivio and from CMR (–0.2%, P ¼ 0.68). The detection of cardiac dysfunction via echocardiography was poor when compared with CMR [Echo EF < 45% (sensitivity 14.3%), Echo EF < 50% (sensitivity 28.6%)]. Sensitivity was substantially better for Vivio-based measurements [EF < 45% or EF < 50% (sensitivity 85.7%)]. Conclusions: This accessible technology has the potential to change the day-to-day practice of clinicians caring for the large number of patients diagnosed with cardiac dysfunction and heart failure each year, allowing real-time monitoring and management of their disease without the lag-time between imaging and interpretation of results.