Abstract Plasmodium knowlesi has been discovered as the fifth species causing malaria in humans. It is a major public health problem in South East Asia especially in Borneo. We report a case of pericardial effusion that rapidly progressing to cardiac tamponade, an atypical presentation of P. knowlesi malaria. Our patient had no underlying known medical illness, presented with high grade fever with chills and rigors, epigastric pain, nausea, vomiting and with poor oral intake. Initial bedside cardiac ultrasound showed minimal pericardial effusion. Within a few hours, she became hypotensive, deteriorated rapidly despite fluid resuscitation requiring mechanical ventilation and inotropic support. Bedside cardiac ultrasound showed cardiac tamponade and pericardiocentesis was done. We highlight the importance of having high level of suspicion for this atypical presentation of cardiac tamponade when a patient is hypotensive in P. knowlesi infection. Prompt diagnosis and management may prevent potentially fatal complication.