The advent of smart cities has paved the way for transformative advancements in healthcare, particularly in the domain of disease diagnosis. In the wake of the COVID-19 pandemic, accurate and timely identification of Pandemic diseases has become paramount. This paper explores the challenges and opportunities in synergizing Artificial Intelligence (AI), Internet of Things (IoT), and Blockchain technologies for diagnosis of Pandemic diseases in smart cities. This study provides an overview of each technology and its relevance to sustainable healthcare in smart cities, emphasizing its potential for analyzing medical data and making informed decisions. We also explore how IoT devices can contribute to disease surveillance, enabling real-time data collection and remote healthcare. Additionally, we discuss the potential of Blockchain in ensuring secure and transparent healthcare systems. Following, the paper study the synergistic potential of integrating AI, IoT, and blockchain, emphasizing how their combined strengths can enhance the accuracy, efficiency, and security of COVID-19 diagnosis systems in smart cities Moreover, the paper highlights the challenges in integrating these technologies and the opportunities for research and implementation, underlining the significance of synergizing AI, IoT, and Blockchain in disease diagnosis in smart cities. The findings demonstrate that the convergence of AI, IoT, and blockchain can enhance the speed and accuracy of diagnosing Pandemic diseases, leading to more effective containment and management strategies.