This paper discusses a personalized heart monitoring system using smart phones and wireless (bio) sensors. We combine ubiquitous computing with mobile health technology to monitor the wellbeing of high risk cardiac patients. The smart phone analyses in real-time the ECG data and determines whether the person needs external help. We focus on two life threatening arrhythmias: Ventricular Fibrillation (VF) and Ventricular Tachycardia (VT). The smart phone can automatically alert the ambulance and pre assigned caregivers when a VF/VT arrhythmia is detected. The system can be personalized to the needs and requirements of the patient. It can be used to give advice (e.g. exercise more) or to reassure the patient when the bio-sensors and environmental data are within predefined ranges.