<b><i>Introduction:</i></b> Experimental research suggests that affect may influence prospective memory performance, but real-life evidence on affect-prospective memory associations is limited. Moreover, most studies have examined the valence dimension of affect in understanding the influence of affect on cognitive performance in daily life, with insufficient consideration of the arousal dimension. To maximize ecological validity, the current study examined the relationships between daily affect and daily prospective memory using repeated daily assessments and the role of resting heart rate on these relationships. We examined both valence and arousal of daily affect by categorizing affect into four dimensions: high-arousal positive affect, low-arousal positive affect, high-arousal negative affect, and low-arousal negative affect. <b><i>Method:</i></b> We examined existing data collected from community-dwelling couples, of which at least one partner had a stroke history. The analytic sample included 111 adults (<i>M</i><sub>age</sub> = 67.46 years, SD = 9.64; 50% women) who provided 1,274 days of data. Among the participants, 58 were living with the effects of a stroke and 53 were partners. Participants completed daily event-based prospective memory tasks (in morning and/or evening questionnaires), reported daily affect in the evening, and wore a wrist-based Fitbit device to monitor resting heart rate over 14 consecutive days. <b><i>Results:</i></b> Results from multilevel models show that, within persons, elevated high-arousal negative affect was associated with worse daily prospective memory performance. In addition, lower resting heart rate attenuated the inverse association between high-arousal negative affect and lowered prospective memory performance. We did not find significant associations of high- or low-arousal positive affect and low-arousal negative affect with daily prospective memory. <b><i>Discussion:</i></b> Our findings are in line with the resource allocation model and the cue-utilization hypothesis in that high-arousal negative affect is detrimental to daily prospective memory performance. Lower resting heart rate may buffer individuals’ prospective memory performance from the influence of high-arousal negative affect. These findings are consistent with the neurovisceral integration model on heart-brain connections, highlighting the possibility that cardiovascular fitness may help maintain prospective memory into older adulthood.